feat: Add album artwork support

- Backend: artwork_filename column on clips table (auto-migration)
- Backend: PATCH /api/clips/{id}/artwork (upload image, 5MB limit)
- Backend: GET /api/clips/{id}/artwork (serve image with correct content-type)
- Backend: DELETE /api/clips/{id}/artwork (remove artwork file + null out DB)
- Backend: DELETE /api/clips/{id} now cascade-removes artwork file
- Frontend: Clip interface includes artwork_filename
- Frontend: Gallery ribbons show artwork thumbnail with hover overlay (play + upload)
- Frontend: Gallery tiles show artwork with hover overlay (play + upload)
- Frontend: DetailPanel shows full artwork with upload/change/remove controls
- Frontend: App.tsx handleUploadArtwork + handleRemoveArtwork handlers
- Storage: /data/artwork/ directory for image files

backend/.env.example

@@ -1 +1,3 @@
-LYRIA_API_KEY=your_api_key_here
+LYRIA_API_KEY=your-api-key-here
+LYRIA_DEFAULT_MODEL=lyria-3-clip-preview
+TZ=America/New_York