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/hooks/useIdle.ts

@@ -0,0 +1,50 @@
+import { useEffect } from 'react';
+import { useUIStore } from '@/stores/uiStore';
+
+type ElectronAPILike = {
+  motion?: { onDetected: (cb: () => void) => () => void };
+};
+
+/**
+ * Tracks touch/mouse/keyboard activity. After `timeoutMs` of no activity,
+ * flips the UI into idle mode (photo frame). Any activity exits idle.
+ * Motion detected by Electron's MotionDetector also cancels idle.
+ */
+export function useIdle(timeoutMs: number) {
+  const isIdle = useUIStore((s) => s.isIdle);
+  const setIdle = useUIStore((s) => s.setIdle);
+
+  useEffect(() => {
+    if (timeoutMs <= 0) return;
+
+    let timer: ReturnType<typeof setTimeout> | null = null;
+
+    const reset = () => {
+      if (timer) clearTimeout(timer);
+      if (useUIStore.getState().isIdle) setIdle(false);
+      timer = setTimeout(() => setIdle(true), timeoutMs);
+    };
+
+    const events: Array<keyof DocumentEventMap> = [
+      'touchstart',
+      'mousedown',
+      'mousemove',
+      'keydown',
+      'wheel',
+    ];
+    for (const e of events) document.addEventListener(e, reset, { passive: true });
+
+    const api = (window as unknown as { electronAPI?: ElectronAPILike }).electronAPI;
+    const unsubMotion = api?.motion?.onDetected?.(() => reset());
+
+    reset();
+
+    return () => {
+      if (timer) clearTimeout(timer);
+      for (const e of events) document.removeEventListener(e, reset);
+      if (unsubMotion) unsubMotion();
+    };
+  }, [timeoutMs, setIdle]);
+
+  return isIdle;
+}