Dance library: bundled clips bind to any rigged model + repertoire + manual BPM

- models/dance_library.glb: skeleton-only GLB with the 13 Mixamo dances,
  loaded at startup and bound BY BONE NAME to whatever rigged GLB the
  user loads — new models dance immediately, no baking needed.
- Repertoire UI (Media tab): checkbox chips of the available clips, the
  director only picks the ticked ones (none = all); persisted.
- 'Aggiungi animazioni': extra .glb clips load directly; .fbx are
  converted on the fly by Blender via a new anim:convert IPC and the
  bundled scripts/fbx2animglb.py (asarUnpacked for packaged builds).
- Manual BPM with TAP tempo: 0 = follow the detected beat, otherwise a
  pure metronome drives the dance clock.

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

preload.js

@@ -38,5 +38,7 @@ contextBridge.exposeInMainWorld('djv', {
   peaks: (path, buckets) => ipcRenderer.invoke('audio:peaks', path, buckets),
   // Ask macOS for camera permission (interactive family) right before use.
   camAccess: () => ipcRenderer.invoke('cam:ensure'),
+  // Convert a Mixamo FBX animation to a library GLB clip (via Blender).
+  convertAnim: (p) => ipcRenderer.invoke('anim:convert', p),
   readFile: (path) => ipcRenderer.invoke('file:read', path)
 });