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/config/environment.ts

@@ -20,6 +20,10 @@ export const env = {
   // Screen management
   screenIdleTimeout: parseInt(import.meta.env.VITE_SCREEN_IDLE_TIMEOUT || '300000', 10),
 
+  // Photo frame idle timeout (ms) - 5 minutes default
+  photoFrameIdleTimeout: parseInt(import.meta.env.VITE_PHOTO_FRAME_IDLE_TIMEOUT || '300000', 10),
+  photoFrameInterval: parseInt(import.meta.env.VITE_PHOTO_FRAME_INTERVAL || '15000', 10),
+
   // Presence detection
   presenceEnabled: import.meta.env.VITE_PRESENCE_DETECTION_ENABLED === 'true',
   presenceConfidenceThreshold: parseFloat(import.meta.env.VITE_PRESENCE_CONFIDENCE_THRESHOLD || '0.6'),