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/app/utils/date.ts

@@ -0,0 +1,48 @@
+/**
+ * Shared date formatting utilities.
+ */
+
+/**
+ * Format date as YYYY-MM-DD in local timezone.
+ */
+export function formatDate(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}`;
+}
+
+/**
+ * Format time from ISO string to HH:MM format.
+ */
+export function formatTime(isoString: string): string {
+  const d = new Date(isoString);
+  return d.toLocaleTimeString("en-US", { 
+    hour: "2-digit", 
+    minute: "2-digit",
+    hour12: false,
+  });
+}
+
+/**
+ * Format datetime from ISO string to a readable format.
+ */
+export function formatDateTime(isoString: string): string {
+  const d = new Date(isoString);
+  return d.toLocaleString("en-US", {
+    weekday: "short",
+    month: "short",
+    day: "numeric",
+    hour: "2-digit",
+    minute: "2-digit",
+    hour12: false,
+  });
+}
+
+/**
+ * Format date for display (e.g., "Mon, Jan 15").
+ */
+export function formatDisplayDate(d: Date): string {
+  return d.toLocaleDateString("en-US", { weekday: "short", month: "short", day: "numeric" });
+}
+