- Add genre, label, copyright fields to ExtTrackMetadata and DownloadResponse
- Add utils.randomUserAgent() for extensions to get random User-Agent strings
- Fix VM race condition panic by adding mutex locks to all provider methods
- Fix Tidal release date fallback when req.ReleaseDate is empty
- Display genre, label, copyright in track metadata screen
- Store extended metadata in download history for persistence
- Add trackGenre, trackLabel, trackCopyright localization strings
- Add extension manager, manifest, runtime, providers, settings
- Add extension provider and UI pages (extensions, detail, priority)
- Add download service picker widget
- Add metadata provider priority page
- Add source field to Track model for extension tracking
- Add skipBuiltInFallback manifest option to skip built-in providers
- Update download queue to use source extension first
- Add extension upgrade support without data loss