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/helpers/date.ts

@@ -0,0 +1,23 @@
+/**
+ * Date formatting helpers for e2e tests.
+ */
+
+/**
+ * Format date as YYYY-MM-DD in local timezone.
+ */
+export 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}`;
+}
+
+/**
+ * Get tomorrow's date string in YYYY-MM-DD format.
+ */
+export function getTomorrowDateStr(): string {
+  const tomorrow = new Date();
+  tomorrow.setDate(tomorrow.getDate() + 1);
+  return formatDateLocal(tomorrow);
+}
+