Add photo frame idle mode and switch to Skylight-style theme

- After 5 min of no touch/motion, dashboard hides behind a fullscreen
  photo slideshow with centered time and date overlay
- Photos loaded from PHOTOS_PATH env var (defaults to ~/Pictures/dashboard)
  via IPC + file:// URLs; traversal-guarded, recursive up to 2 levels
- Motion or touch exits idle back to dashboard
- Theme repainted warm cream / sage / stone ink with Nunito font and
  rounded cards; dark tokens kept so component classes still resolve
- Adds PHOTO_FRAME.md with Samba cifs mount + systemd env instructions

src/App.tsx

@@ -11,7 +11,9 @@ import { CameraOverlay } from '@/components/cameras';
 import { CameraFeed } from '@/components/cameras/CameraFeed';
 import { JellyfinOverlay } from '@/components/media';
 import { GlobalKeyboard } from '@/components/keyboard';
+import { PhotoFrame } from '@/components/photoframe';
 import { useHomeAssistant } from '@/hooks';
+import { useIdle } from '@/hooks/useIdle';
 // Motion detection now runs in Electron main process (MotionDetector.ts)
 // import { useSimpleMotion } from '@/hooks/useSimpleMotion';
 import { useHAStore, useEntityAttribute } from '@/stores/haStore';
@@ -182,6 +184,7 @@ export default function App() {
   const thermostatsOverlayOpen = useUIStore((state) => state.thermostatsOverlayOpen);
   const mediaOverlayOpen = useUIStore((state) => state.mediaOverlayOpen);
   const { isOpen: cameraOverlayOpen } = useCameraOverlay();
+  const isIdle = useIdle(env.photoFrameIdleTimeout);
 
   // Person detection alert state
   const personDetectionEntities = useSettingsStore((state) => state.config.personDetectionEntities);
@@ -334,6 +337,7 @@ export default function App() {
       {mediaOverlayOpen && <JellyfinOverlay />}
       {cameraOverlayOpen && <CameraOverlay />}
       {settingsOpen && <SettingsPanel />}
+      {isIdle && !alertCamera && <PhotoFrame intervalMs={env.photoFrameInterval} />}
       {alertCamera && <PersonAlert cameraName={alertCamera} onClose={closePersonAlert} />}
       <GlobalKeyboard />
     </>