Extract duplicate date formatting functions to shared utilities

- Created frontend/app/utils/date.ts with formatDate, formatTime, formatDateTime, formatDisplayDate
- Created frontend/e2e/helpers/date.ts with formatDateLocal, getTomorrowDateStr
- Updated all frontend pages and e2e tests to use shared utilities
- Removed duplicate date formatting code from 6 files

frontend/e2e/availability.spec.ts

@@ -1,4 +1,5 @@
 import { test, expect, Page } from "@playwright/test";
+import { formatDateLocal, getTomorrowDateStr } from "./helpers/date";
 
 /**
  * Availability Page E2E Tests
@@ -45,20 +46,6 @@ function getTomorrowDisplay(): string {
   return tomorrow.toLocaleDateString("en-US", { weekday: "short", month: "short", day: "numeric" });
 }
 
-// Helper to get a date string in YYYY-MM-DD format using local timezone
-function formatDateLocal(d: Date): string {
-  const year = d.getFullYear();
-  const month = String(d.getMonth() + 1).padStart(2, "0");
-  const day = String(d.getDate()).padStart(2, "0");
-  return `${year}-${month}-${day}`;
-}
-
-function getTomorrowDateStr(): string {
-  const tomorrow = new Date();
-  tomorrow.setDate(tomorrow.getDate() + 1);
-  return formatDateLocal(tomorrow);
-}
-
 test.describe("Availability Page - Admin Access", () => {
   test.beforeEach(async ({ page }) => {
     await clearAuth(page);