Refactors date and file formatting utilities

refactor(utils): consolidate date and file size formatting

Extracts formatting logic into dedicated utility functions to improve
code maintainability and consistency across components.

Changes:
- Consolidate date formatting functions (formatRelativeTime, etc.)
- Consolidate file size formatting into single formatFileSize utility
- Fix file size calculation errors
- Update UI components to use new utilities
- Change "ASAP" to "Waiting" for unscheduled queue items

Tests:
- Add comprehensive unit tests for date utilities
- Add unit tests for file size formatting

frontend/src/utils/date.ts

@@ -424,3 +424,64 @@ export function formatDuration(seconds: number | null | undefined): string {
   
   return hours > 0 ? `${hours}h ${minutes}m` : `${minutes}m`;
 }
+
+type TranslateFunction = (key: string, options?: Record<string, unknown>) => string;
+
+/**
+ * Format a date string as a human-readable relative time expression.
+ *
+ * @param dateStr - UTC date string, or null
+ * @param timeFormat - Time format preference ('12h', '24h', or 'system')
+ * @param t - Optional translation function for i18n support
+ * @returns Relative string (e.g., "5m ago", "in 2h", "3d ago") or formatted date if older than 7 days
+ */
+export function formatRelativeTime(
+  dateStr: string | null,
+  timeFormat: TimeFormat = 'system',
+  t?: TranslateFunction
+): string {
+  if (!dateStr) return t?.('time.unknown') ?? '-';
+
+  const date = parseUTCDate(dateStr);
+  if (!date) return t?.('time.unknown') ?? '-';
+
+  const now = new Date();
+  const diffMs = date.getTime() - now.getTime();
+  const isPast = diffMs < 0;
+  const absDiffMs = Math.abs(diffMs);
+
+  const minutes = Math.floor(absDiffMs / 60000);
+  const hours = Math.floor(absDiffMs / 3600000);
+  const days = Math.floor(absDiffMs / 86400000);
+
+  // Less than 1 minute
+  if (minutes < 1) {
+    return isPast
+      ? t?.('time.justNow') ?? 'Just now'
+      : t?.('time.now') ?? 'Now';
+  }
+
+  // Less than 1 hour
+  if (hours < 1) {
+    return isPast
+      ? t?.('time.minsAgo', { count: minutes }) ?? `${minutes}m ago`
+      : t?.('time.inMins', { count: minutes }) ?? `in ${minutes}m`;
+  }
+
+  // Less than 1 day
+  if (days < 1) {
+    return isPast
+      ? t?.('time.hoursAgo', { count: hours }) ?? `${hours}h ago`
+      : t?.('time.inHours', { count: hours }) ?? `in ${hours}h`;
+  }
+
+  // Less than 7 days
+  if (days < 7) {
+    return isPast
+      ? t?.('time.daysAgo', { count: days }) ?? `${days}d ago`
+      : t?.('time.inDays', { count: days }) ?? `in ${days}d`;
+  }
+
+  // Older than 7 days
+  return formatDateTime(dateStr, timeFormat);
+}