Interactive camera family: webcam motion pushes physical balls on screen

New 'Interattivo Palle' family (interactive.js): frame-differencing motion map
from the webcam, ball physics (push-away forces, collisions, beat kicks),
palette-tinted rendering with motion mist. Camera is requested lazily and
released when switching preset; mouse/touch fallback when unavailable.
Excluded from Auto VJ so the camera never turns on by itself.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

preload.js

@@ -36,5 +36,7 @@ contextBridge.exposeInMainWorld('djv', {
   exportPlaylist: (data) => ipcRenderer.invoke('playlist:export', data),
   importPlaylist: () => ipcRenderer.invoke('playlist:import'),
   peaks: (path, buckets) => ipcRenderer.invoke('audio:peaks', path, buckets),
+  // Ask macOS for camera permission (interactive family) right before use.
+  camAccess: () => ipcRenderer.invoke('cam:ensure'),
   readFile: (path) => ipcRenderer.invoke('file:read', path)
 });