refactor(frontend): consolidate shared styles into centralized style system

- Create comprehensive shared.ts with design tokens and categorized styles:
  - layoutStyles: main, loader, content variants
  - cardStyles: card, tableCard, cardHeader
  - tableStyles: complete table styling
  - paginationStyles: pagination controls
  - formStyles: inputs, labels, errors
  - buttonStyles: primary, secondary, accent, danger variants
  - badgeStyles: status badges with color variants
  - bannerStyles: error/success banners
  - modalStyles: modal overlay and content
  - toastStyles: toast notifications
  - utilityStyles: divider, emptyState, etc.

- Refactor all page components to use shared styles:
  - page.tsx (counter)
  - audit/page.tsx
  - booking/page.tsx
  - appointments/page.tsx
  - profile/page.tsx
  - invites/page.tsx
  - admin/invites/page.tsx
  - admin/availability/page.tsx

- Reduce code duplication significantly (each page now has only
  truly page-specific styles)
- Maintain backwards compatibility with sharedStyles export

frontend/app/audit/page.tsx

@@ -3,7 +3,7 @@
 import { useEffect, useState, useCallback } from "react";
 import { Permission } from "../auth-context";
 import { api } from "../api";
-import { sharedStyles } from "../styles/shared";
+import { layoutStyles, cardStyles, tableStyles, paginationStyles } from "../styles/shared";
 import { Header } from "../components/Header";
 import { useRequireAuth } from "../hooks/useRequireAuth";
 import { components } from "../generated/api";
@@ -68,8 +68,8 @@ export default function AuditPage() {
 
   if (isLoading) {
     return (
-      <main style={styles.main}>
-        <div style={styles.loader}>Loading...</div>
+      <main style={layoutStyles.main}>
+        <div style={layoutStyles.loader}>Loading...</div>
       </main>
     );
   }
@@ -79,47 +79,47 @@ export default function AuditPage() {
   }
 
   return (
-    <main style={styles.main}>
+    <main style={layoutStyles.main}>
       <Header currentPage="audit" />
 
-      <div style={styles.content}>
+      <div style={layoutStyles.contentScrollable}>
         <div style={styles.tablesContainer}>
           {/* Counter Records Table */}
-          <div style={styles.tableCard}>
-            <div style={styles.tableHeader}>
-              <h2 style={styles.tableTitle}>Counter Activity</h2>
-              <span style={styles.totalCount}>{counterData?.total ?? 0} records</span>
+          <div style={cardStyles.tableCard}>
+            <div style={tableStyles.tableHeader}>
+              <h2 style={tableStyles.tableTitle}>Counter Activity</h2>
+              <span style={tableStyles.totalCount}>{counterData?.total ?? 0} records</span>
             </div>
-            <div style={styles.tableWrapper}>
-              <table style={styles.table}>
+            <div style={tableStyles.tableWrapper}>
+              <table style={tableStyles.table}>
                 <thead>
                   <tr>
-                    <th style={styles.th}>User</th>
-                    <th style={styles.th}>Before</th>
-                    <th style={styles.th}>After</th>
-                    <th style={styles.th}>Date</th>
+                    <th style={tableStyles.th}>User</th>
+                    <th style={tableStyles.th}>Before</th>
+                    <th style={tableStyles.th}>After</th>
+                    <th style={tableStyles.th}>Date</th>
                   </tr>
                 </thead>
                 <tbody>
                   {counterError && (
                     <tr>
-                      <td colSpan={4} style={styles.errorRow}>
+                      <td colSpan={4} style={tableStyles.errorRow}>
                         {counterError}
                       </td>
                     </tr>
                   )}
                   {!counterError &&
                     counterData?.records.map((record) => (
-                      <tr key={record.id} style={styles.tr}>
-                        <td style={styles.td}>{record.user_email}</td>
-                        <td style={styles.tdNum}>{record.value_before}</td>
-                        <td style={styles.tdNum}>{record.value_after}</td>
-                        <td style={styles.tdDate}>{formatDate(record.created_at)}</td>
+                      <tr key={record.id} style={tableStyles.tr}>
+                        <td style={tableStyles.td}>{record.user_email}</td>
+                        <td style={tableStyles.tdNum}>{record.value_before}</td>
+                        <td style={tableStyles.tdNum}>{record.value_after}</td>
+                        <td style={tableStyles.tdDate}>{formatDate(record.created_at)}</td>
                       </tr>
                     ))}
                   {!counterError && (!counterData || counterData.records.length === 0) && (
                     <tr>
-                      <td colSpan={4} style={styles.emptyRow}>
+                      <td colSpan={4} style={tableStyles.emptyRow}>
                         No records yet
                       </td>
                     </tr>
@@ -128,21 +128,21 @@ export default function AuditPage() {
               </table>
             </div>
             {counterData && counterData.total_pages > 1 && (
-              <div style={styles.pagination}>
+              <div style={paginationStyles.pagination}>
                 <button
                   onClick={() => setCounterPage((p) => Math.max(1, p - 1))}
                   disabled={counterPage === 1}
-                  style={styles.pageBtn}
+                  style={paginationStyles.pageBtn}
                 >
                   ←
                 </button>
-                <span style={styles.pageInfo}>
+                <span style={paginationStyles.pageInfo}>
                   {counterPage} / {counterData.total_pages}
                 </span>
                 <button
                   onClick={() => setCounterPage((p) => Math.min(counterData.total_pages, p + 1))}
                   disabled={counterPage === counterData.total_pages}
-                  style={styles.pageBtn}
+                  style={paginationStyles.pageBtn}
                 >
                   →
                 </button>
@@ -151,43 +151,43 @@ export default function AuditPage() {
           </div>
 
           {/* Sum Records Table */}
-          <div style={styles.tableCard}>
-            <div style={styles.tableHeader}>
-              <h2 style={styles.tableTitle}>Sum Activity</h2>
-              <span style={styles.totalCount}>{sumData?.total ?? 0} records</span>
+          <div style={cardStyles.tableCard}>
+            <div style={tableStyles.tableHeader}>
+              <h2 style={tableStyles.tableTitle}>Sum Activity</h2>
+              <span style={tableStyles.totalCount}>{sumData?.total ?? 0} records</span>
             </div>
-            <div style={styles.tableWrapper}>
-              <table style={styles.table}>
+            <div style={tableStyles.tableWrapper}>
+              <table style={tableStyles.table}>
                 <thead>
                   <tr>
-                    <th style={styles.th}>User</th>
-                    <th style={styles.th}>A</th>
-                    <th style={styles.th}>B</th>
-                    <th style={styles.th}>Result</th>
-                    <th style={styles.th}>Date</th>
+                    <th style={tableStyles.th}>User</th>
+                    <th style={tableStyles.th}>A</th>
+                    <th style={tableStyles.th}>B</th>
+                    <th style={tableStyles.th}>Result</th>
+                    <th style={tableStyles.th}>Date</th>
                   </tr>
                 </thead>
                 <tbody>
                   {sumError && (
                     <tr>
-                      <td colSpan={5} style={styles.errorRow}>
+                      <td colSpan={5} style={tableStyles.errorRow}>
                         {sumError}
                       </td>
                     </tr>
                   )}
                   {!sumError &&
                     sumData?.records.map((record) => (
-                      <tr key={record.id} style={styles.tr}>
-                        <td style={styles.td}>{record.user_email}</td>
-                        <td style={styles.tdNum}>{record.a}</td>
-                        <td style={styles.tdNum}>{record.b}</td>
+                      <tr key={record.id} style={tableStyles.tr}>
+                        <td style={tableStyles.td}>{record.user_email}</td>
+                        <td style={tableStyles.tdNum}>{record.a}</td>
+                        <td style={tableStyles.tdNum}>{record.b}</td>
                         <td style={styles.tdResult}>{record.result}</td>
-                        <td style={styles.tdDate}>{formatDate(record.created_at)}</td>
+                        <td style={tableStyles.tdDate}>{formatDate(record.created_at)}</td>
                       </tr>
                     ))}
                   {!sumError && (!sumData || sumData.records.length === 0) && (
                     <tr>
-                      <td colSpan={5} style={styles.emptyRow}>
+                      <td colSpan={5} style={tableStyles.emptyRow}>
                         No records yet
                       </td>
                     </tr>
@@ -196,21 +196,21 @@ export default function AuditPage() {
               </table>
             </div>
             {sumData && sumData.total_pages > 1 && (
-              <div style={styles.pagination}>
+              <div style={paginationStyles.pagination}>
                 <button
                   onClick={() => setSumPage((p) => Math.max(1, p - 1))}
                   disabled={sumPage === 1}
-                  style={styles.pageBtn}
+                  style={paginationStyles.pageBtn}
                 >
                   ←
                 </button>
-                <span style={styles.pageInfo}>
+                <span style={paginationStyles.pageInfo}>
                   {sumPage} / {sumData.total_pages}
                 </span>
                 <button
                   onClick={() => setSumPage((p) => Math.min(sumData.total_pages, p + 1))}
                   disabled={sumPage === sumData.total_pages}
-                  style={styles.pageBtn}
+                  style={paginationStyles.pageBtn}
                 >
                   →
                 </button>
@@ -223,13 +223,8 @@ export default function AuditPage() {
   );
 }
 
-const pageStyles: Record<string, React.CSSProperties> = {
-  // Override content for audit-specific layout
-  content: {
-    flex: 1,
-    padding: "2rem",
-    overflowY: "auto",
-  },
+// Page-specific styles only
+const styles: Record<string, React.CSSProperties> = {
   tablesContainer: {
     display: "flex",
     flexDirection: "column",
@@ -237,64 +232,6 @@ const pageStyles: Record<string, React.CSSProperties> = {
     maxWidth: "1200px",
     margin: "0 auto",
   },
-  tableCard: {
-    background: "rgba(255, 255, 255, 0.03)",
-    backdropFilter: "blur(10px)",
-    border: "1px solid rgba(255, 255, 255, 0.08)",
-    borderRadius: "20px",
-    padding: "1.5rem",
-    boxShadow: "0 25px 50px -12px rgba(0, 0, 0, 0.5)",
-  },
-  tableHeader: {
-    display: "flex",
-    justifyContent: "space-between",
-    alignItems: "center",
-    marginBottom: "1rem",
-  },
-  tableTitle: {
-    fontFamily: "'Instrument Serif', Georgia, serif",
-    fontSize: "1.5rem",
-    fontWeight: 400,
-    color: "#fff",
-    margin: 0,
-  },
-  totalCount: {
-    fontFamily: "'DM Sans', system-ui, sans-serif",
-    fontSize: "0.875rem",
-    color: "rgba(255, 255, 255, 0.4)",
-  },
-  tableWrapper: {
-    overflowX: "auto",
-  },
-  table: {
-    width: "100%",
-    borderCollapse: "collapse",
-    fontFamily: "'DM Sans', system-ui, sans-serif",
-  },
-  th: {
-    textAlign: "left",
-    padding: "0.75rem 1rem",
-    fontSize: "0.75rem",
-    fontWeight: 600,
-    color: "rgba(255, 255, 255, 0.4)",
-    textTransform: "uppercase",
-    letterSpacing: "0.05em",
-    borderBottom: "1px solid rgba(255, 255, 255, 0.08)",
-  },
-  tr: {
-    borderBottom: "1px solid rgba(255, 255, 255, 0.04)",
-  },
-  td: {
-    padding: "0.875rem 1rem",
-    fontSize: "0.875rem",
-    color: "rgba(255, 255, 255, 0.7)",
-  },
-  tdNum: {
-    padding: "0.875rem 1rem",
-    fontSize: "0.875rem",
-    color: "rgba(255, 255, 255, 0.9)",
-    fontFamily: "'DM Sans', monospace",
-  },
   tdResult: {
     padding: "0.875rem 1rem",
     fontSize: "0.875rem",
@@ -302,48 +239,4 @@ const pageStyles: Record<string, React.CSSProperties> = {
     fontWeight: 600,
     fontFamily: "'DM Sans', monospace",
   },
-  tdDate: {
-    padding: "0.875rem 1rem",
-    fontSize: "0.75rem",
-    color: "rgba(255, 255, 255, 0.4)",
-  },
-  emptyRow: {
-    padding: "2rem 1rem",
-    textAlign: "center",
-    color: "rgba(255, 255, 255, 0.3)",
-    fontSize: "0.875rem",
-  },
-  errorRow: {
-    padding: "2rem 1rem",
-    textAlign: "center",
-    color: "#f87171",
-    fontSize: "0.875rem",
-  },
-  pagination: {
-    display: "flex",
-    justifyContent: "center",
-    alignItems: "center",
-    gap: "1rem",
-    marginTop: "1rem",
-    paddingTop: "1rem",
-    borderTop: "1px solid rgba(255, 255, 255, 0.06)",
-  },
-  pageBtn: {
-    fontFamily: "'DM Sans', system-ui, sans-serif",
-    padding: "0.5rem 1rem",
-    fontSize: "1rem",
-    background: "rgba(255, 255, 255, 0.05)",
-    color: "rgba(255, 255, 255, 0.7)",
-    border: "1px solid rgba(255, 255, 255, 0.1)",
-    borderRadius: "8px",
-    cursor: "pointer",
-    transition: "all 0.2s",
-  },
-  pageInfo: {
-    fontFamily: "'DM Sans', system-ui, sans-serif",
-    fontSize: "0.875rem",
-    color: "rgba(255, 255, 255, 0.5)",
-  },
 };
-
-const styles = { ...sharedStyles, ...pageStyles };