feat(playlists): add local playlist enhancements

- Add playlist settings table for storing local-only features per playlist
- Add playlist local tracks table for mixing local tracks into Qobuz playlists
- Implement search within playlist (filters by title, artist, album)
- Add custom sorting (by title, artist, album, duration, ascending/descending)
- Add custom artwork selection with file picker
- Create .env.example for Last.fm credentials setup
- Update README with environment configuration instructions

.env.example

@@ -0,0 +1,8 @@
+# Last.fm API Configuration
+# Create your own Last.fm API application at: https://www.last.fm/api/account/create
+# These credentials are required for scrobbling functionality
+
+LAST_FM_API_KEY=your_api_key_here
+LAST_FM_API_SHARED_SECRET=your_shared_secret_here
+LAST_FM_APP_NAME=your_app_name
+LAST_FM_APP_REGISTER=your_lastfm_username