- Added toggle buttons and stat counters to `video-modal.html`.
- Updated `VideoModal.js` to manage toggle visibility (show if either source exists, disable unavailable option) and dispatch `playback:switch-source` events.
- Updated `app.js` to handle source switching by restarting playback with a `forcedSource`.
- Updated `playbackService.js` to respect `forcedSource` by bypassing probe logic when a specific source is requested.
