Fix QA findings: rename ambient component, add clock tab-resume sync

W-02: Renamed layout/AmbientBackground → AppAmbientBackground to avoid
naming collision with auth/AmbientBackground (IDE auto-import confusion).

S-01: Added visibilitychange listener to re-sync clock after tab
sleep/resume. Previously the interval would drift after laptop sleep
or long tab backgrounding.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/dashboard/DashboardPage.tsx

@@ -44,16 +44,35 @@ export default function DashboardPage() {
   const dropdownRef = useRef<HTMLDivElement>(null);
   const [clockNow, setClockNow] = useState(() => new Date());
 
-  // Live clock — synced to the minute boundary
+  // Live clock — synced to the minute boundary, re-syncs after tab sleep/resume
   useEffect(() => {
     let intervalId: ReturnType<typeof setInterval>;
-    // Wait until the next :00 second mark, then tick every 60s
+    let timeoutId: ReturnType<typeof setTimeout>;
+
+    function startClock() {
+      clearTimeout(timeoutId);
+      clearInterval(intervalId);
+      setClockNow(new Date());
       const msUntilNextMinute = (60 - new Date().getSeconds()) * 1000 - new Date().getMilliseconds();
-    const timeoutId = setTimeout(() => {
+      timeoutId = setTimeout(() => {
         setClockNow(new Date());
         intervalId = setInterval(() => setClockNow(new Date()), 60_000);
       }, msUntilNextMinute);
-    return () => { clearTimeout(timeoutId); clearInterval(intervalId); };
+    }
+
+    startClock();
+
+    // Re-sync when tab becomes visible again (after sleep/background throttle)
+    function handleVisibility() {
+      if (document.visibilityState === 'visible') startClock();
+    }
+    document.addEventListener('visibilitychange', handleVisibility);
+
+    return () => {
+      clearTimeout(timeoutId);
+      clearInterval(intervalId);
+      document.removeEventListener('visibilitychange', handleVisibility);
+    };
   }, []);
 
   // Click outside to close dropdown

frontend/src/components/layout/AppAmbientBackground.tsx

@@ -8,7 +8,7 @@
  * Also renders a noise texture for tactile depth and a radial vignette
  * to darken edges and draw focus to center content.
  */
-export default function AmbientBackground() {
+export default function AppAmbientBackground() {
   return (
     <div className="pointer-events-none absolute inset-0 z-0 overflow-hidden" aria-hidden="true">
       {/* Animated gradient orbs — oversized so drift never clips at visible edges */}

frontend/src/components/layout/AppLayout.tsx

@@ -7,7 +7,7 @@ import { LockProvider } from '@/hooks/useLock';
 import { NotificationProvider } from '@/hooks/useNotifications';
 import { Button } from '@/components/ui/button';
 import Sidebar from './Sidebar';
-import AmbientBackground from './AmbientBackground';
+import AppAmbientBackground from './AppAmbientBackground';
 import LockOverlay from './LockOverlay';
 import NotificationToaster from '@/components/notifications/NotificationToaster';
 
@@ -35,7 +35,7 @@ export default function AppLayout() {
               onMobileClose={() => setMobileOpen(false)}
             />
             <div className="flex-1 flex flex-col overflow-hidden relative ambient-glass">
-              <AmbientBackground />
+              <AppAmbientBackground />
               {/* Mobile header */}
               <div className="relative z-10 flex md:hidden items-center h-14 border-b bg-card px-4">
                 <Button variant="ghost" size="icon" onClick={() => setMobileOpen(true)}>