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

electron/preload.ts

@@ -17,6 +17,9 @@ export interface ElectronAPI {
     startStream: (rtspUrl: string) => Promise<boolean>;
     stopStream: () => Promise<boolean>;
   };
+  motion: {
+    onDetected: (callback: () => void) => () => void;
+  };
   app: {
     quit: () => void;
     toggleFullscreen: () => void;
@@ -26,6 +29,11 @@ export interface ElectronAPI {
     getStoredToken: () => Promise<string | null>;
     getJellyfinApiKey: () => Promise<string | null>;
   };
+  photos: {
+    list: () => Promise<string[]>;
+    getDir: () => Promise<string>;
+    getUrl: (relative: string) => Promise<string | null>;
+  };
 }
 
 const electronAPI: ElectronAPI = {
@@ -53,6 +61,13 @@ const electronAPI: ElectronAPI = {
     startStream: (rtspUrl: string) => ipcRenderer.invoke('frigate:startStream', rtspUrl),
     stopStream: () => ipcRenderer.invoke('frigate:stopStream'),
   },
+  motion: {
+    onDetected: (callback: () => void) => {
+      const handler = (_event: IpcRendererEvent) => callback();
+      ipcRenderer.on('motion:detected', handler);
+      return () => ipcRenderer.removeListener('motion:detected', handler);
+    },
+  },
   app: {
     quit: () => ipcRenderer.invoke('app:quit'),
     toggleFullscreen: () => ipcRenderer.invoke('app:toggleFullscreen'),
@@ -62,6 +77,11 @@ const electronAPI: ElectronAPI = {
     getStoredToken: () => ipcRenderer.invoke('config:getStoredToken'),
     getJellyfinApiKey: () => ipcRenderer.invoke('config:getJellyfinApiKey'),
   },
+  photos: {
+    list: () => ipcRenderer.invoke('photos:list'),
+    getDir: () => ipcRenderer.invoke('photos:getDir'),
+    getUrl: (relative: string) => ipcRenderer.invoke('photos:getUrl', relative),
+  },
 };
 
 contextBridge.exposeInMainWorld('electronAPI', electronAPI);