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

.env.example

@@ -20,3 +20,13 @@ VITE_PRESENCE_CONFIDENCE_THRESHOLD=0.6
 # Frigate Streaming from built-in camera
 VITE_FRIGATE_STREAM_ENABLED=true
 VITE_FRIGATE_RTSP_OUTPUT=rtsp://192.168.1.241:8554/command_center
+
+# Photo Frame (shown after inactivity)
+# Idle timeout in ms before photo frame takes over (default 5 min)
+VITE_PHOTO_FRAME_IDLE_TIMEOUT=300000
+# Seconds between photo transitions
+VITE_PHOTO_FRAME_INTERVAL=15000
+# Path to photos directory on the kiosk (set via PHOTOS_PATH env var for the
+# Electron process, not via Vite). Typically a mounted Samba share. Example:
+#   PHOTOS_PATH=/mnt/family-photos
+# If unset, defaults to ~/Pictures/dashboard on the kiosk user's account.