Fix timezone display: parse UTC timestamps correctly in logs pages

Agent-Logs-Url: https://github.com/christianlouis/InboxConverge/sessions/70a69601-e0b9-4a00-bcf4-0a85d2bdf6cb

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/src/app/admin/logs/page.tsx

@@ -8,6 +8,7 @@ import { useAuthStore } from '@/store/authStore';
 import { useRouter } from 'next/navigation';
 import { useEffect } from 'react';
 import { adminApi, AdminProcessingRun } from '@/lib/api';
+import { parseUTC } from '@/lib/date-utils';
 import {
   Activity,
   ChevronLeft,
@@ -31,7 +32,7 @@ function formatDuration(seconds?: number | null): string {
 }
 
 function formatDate(iso: string): string {
-  return new Date(iso).toLocaleString(undefined, {
+  return parseUTC(iso).toLocaleString(undefined, {
     dateStyle: 'short',
     timeStyle: 'medium',
   });

frontend/src/app/logs/page.tsx

@@ -5,6 +5,7 @@ import { AuthGuard } from '@/components/AuthGuard';
 import { DashboardLayout } from '@/components/DashboardLayout';
 import { useQuery } from '@tanstack/react-query';
 import { processingRunsApi, mailAccountsApi, MailAccount, ProcessingRun, ProcessingLog } from '@/lib/api';
+import { parseUTC } from '@/lib/date-utils';
 import {
   Inbox,
   ChevronLeft,
@@ -20,7 +21,7 @@ import {
 
 function formatRelative(iso?: string | null): string {
   if (!iso) return 'Never';
-  const diff = Date.now() - new Date(iso).getTime();
+  const diff = Date.now() - parseUTC(iso).getTime();
   const minutes = Math.floor(diff / 60000);
   if (minutes < 1) return 'Just now';
   if (minutes < 60) return `${minutes}m ago`;
@@ -30,7 +31,7 @@ function formatRelative(iso?: string | null): string {
 }
 
 function formatDate(iso: string): string {
-  return new Date(iso).toLocaleString(undefined, {
+  return parseUTC(iso).toLocaleString(undefined, {
     dateStyle: 'short',
     timeStyle: 'medium',
   });

frontend/src/lib/date-utils.ts

@@ -0,0 +1,16 @@
+/**
+ * Parse an ISO-8601 datetime string as UTC.
+ *
+ * The backend stores all timestamps in UTC.  When the serialised string has no
+ * explicit timezone indicator (no trailing `Z` or `±HH:MM` offset), JavaScript's
+ * `Date` constructor treats it as *local* time.  For clients in UTC+N this
+ * shifts every timestamp N hours into the past, causing "Xh ago" relative
+ * labels and `toLocaleString()` absolute dates to be wrong.
+ *
+ * This helper appends `Z` to any timezone-naive ISO string so it is always
+ * interpreted as UTC.  Strings that already carry timezone info are passed
+ * through unchanged.
+ */
+export function parseUTC(iso: string): Date {
+  return new Date(/Z|[+-]\d{2}:?\d{2}$/.test(iso) ? iso : iso + 'Z');
+}