- Add ProGuard rules for Flutter plugins (path_provider, local_notifications, receive_sharing_intent, etc.)
- Upgrade Go to 1.25.6 for 16KB page alignment support
- Expand ProGuard rules for Go backend and Kotlin coroutines
- Fix R8 stripping plugin implementations in release builds
- 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