feat: improve track selection and restore audio-only for combined UMP

[kikoso]

This PR restores full functionality to the "Audio Only" mode when using combined UMP streams by implementing a new adapter-based bridging system that allows muxed video sources to be wrapped as audio-only equivalents. With this approach, the player can now correctly initialize playback and preserve request modifiers even when dedicated audio streams are missing due to bot-detection avoidance measures.

Together with this restoration, the update enhances track selection by integrating persistent audio and subtitle language preferences directly into the underlying ExoPlayer track selector, ensuring that internal manifest tracks are automatically prioritized based on the user's primary language and sticky subtitle settings. The user interface has also been refined in both the Video Detail and Short views to correctly display these internal manifest tracks in the quality selection menu, where a more robust deduplication algorithm ensures the list remains concise by showing only the best bitrate options per language.

Finally, the implementation resolves a bug where DASH audio manifests were being incorrectly assigned to video variables and improves overall stability through safer null-handling and reference management across the JavaScript-based source models.

Testing:

• Set a primary language
• Verify a UMP video plays on the primary language, if available.
• Toggle "Prefer Original language"
• Verify a UMP video plays on the original language.
• Change language of video and audio in the UMP video settings, and verify it works.
• Change subtitles and verify it works.