refactor: extract shared formatEur and getTradeStatusDisplay utilities

- Create frontend/app/utils/exchange.ts with shared formatting functions
- Update exchange/page.tsx to use shared formatEur
- Update trades/page.tsx to use shared formatEur and getTradeStatusDisplay
- Update admin/trades/page.tsx to use shared formatEur and getTradeStatusDisplay
- SatsDisplay was already extracted (confirmed it's in components/SatsDisplay.tsx)

frontend/app/trades/page.tsx

@@ -9,6 +9,7 @@ import { SatsDisplay } from "../components/SatsDisplay";
 import { useRequireAuth } from "../hooks/useRequireAuth";
 import { components } from "../generated/api";
 import { formatDateTime } from "../utils/date";
+import { formatEur, getTradeStatusDisplay } from "../utils/exchange";
 import {
   layoutStyles,
   typographyStyles,
@@ -19,61 +20,6 @@ import {
 
 type ExchangeResponse = components["schemas"]["ExchangeResponse"];
 
-/**
- * Format EUR amount from cents to display string
- */
-function formatEur(cents: number): string {
-  return `€${(cents / 100).toLocaleString("de-DE")}`;
-}
-
-/**
- * Get status display properties
- */
-function getTradeStatusDisplay(status: string): {
-  text: string;
-  bgColor: string;
-  textColor: string;
-} {
-  switch (status) {
-    case "booked":
-      return {
-        text: "Pending",
-        bgColor: "rgba(99, 102, 241, 0.2)",
-        textColor: "rgba(129, 140, 248, 0.9)",
-      };
-    case "completed":
-      return {
-        text: "Completed",
-        bgColor: "rgba(34, 197, 94, 0.2)",
-        textColor: "rgba(34, 197, 94, 0.9)",
-      };
-    case "cancelled_by_user":
-      return {
-        text: "Cancelled",
-        bgColor: "rgba(239, 68, 68, 0.2)",
-        textColor: "rgba(239, 68, 68, 0.9)",
-      };
-    case "cancelled_by_admin":
-      return {
-        text: "Cancelled by Admin",
-        bgColor: "rgba(239, 68, 68, 0.2)",
-        textColor: "rgba(239, 68, 68, 0.9)",
-      };
-    case "no_show":
-      return {
-        text: "No Show",
-        bgColor: "rgba(251, 146, 60, 0.2)",
-        textColor: "rgba(251, 146, 60, 0.9)",
-      };
-    default:
-      return {
-        text: status,
-        bgColor: "rgba(255, 255, 255, 0.1)",
-        textColor: "rgba(255, 255, 255, 0.6)",
-      };
-  }
-}
-
 export default function TradesPage() {
   const { user, isLoading, isAuthorized } = useRequireAuth({
     requiredPermission: Permission.VIEW_OWN_EXCHANGES,