feat: add getLocalDateKey, formatDayHeader, formatTimeOnly date helpers

Made-with: Cursor

frontend/src/utils/dateUtils.js

@@ -56,3 +56,44 @@ export function isSunday(sqliteTimestamp) {
   return parseUTCTimestamp(sqliteTimestamp).getDay() === 0;
 }
 
+/**
+ * Get a locale-independent date key for grouping sessions by local calendar day
+ * @param {string} sqliteTimestamp
+ * @returns {string} - e.g., "2026-03-23"
+ */
+export function getLocalDateKey(sqliteTimestamp) {
+  const d = parseUTCTimestamp(sqliteTimestamp);
+  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 a SQLite timestamp as a day header string (e.g., "Sunday, Mar 23, 2026")
+ * @param {string} sqliteTimestamp
+ * @returns {string}
+ */
+export function formatDayHeader(sqliteTimestamp) {
+  const d = parseUTCTimestamp(sqliteTimestamp);
+  return d.toLocaleDateString(undefined, {
+    weekday: 'long',
+    year: 'numeric',
+    month: 'short',
+    day: 'numeric',
+  });
+}
+
+/**
+ * Format a SQLite timestamp as a time-only string (e.g., "7:30 PM")
+ * @param {string} sqliteTimestamp
+ * @returns {string}
+ */
+export function formatTimeOnly(sqliteTimestamp) {
+  const d = parseUTCTimestamp(sqliteTimestamp);
+  return d.toLocaleTimeString(undefined, {
+    hour: 'numeric',
+    minute: '2-digit',
+  });
+}
+