1076 feature audio track selector for video player

[LeviXIII]

Summary

Closes #1076

Adds an audio language selector to the top-right corner of the video if it has multiple audio tracks. If only one track exists, it is not shown.

Changes

• When a video source exposes more than one audio track (HLS .m3u8 with multiple dubs), an Audio language selector appears on the player.
• The selector lists each available audio track by its language/name from the stream manifest, with the currently active track indicated.
• Selecting a language switches the spoken audio without restarting or breaking playback.
• The selector is hidden for sources with a single audio track (e.g. plain MP4s), so nothing changes for existing single-track videos.
• Switching the audio-language track has no effect on user-recorded per-cell dub audio; recording and dub playback continue to work as before.
• The control is visually unobtrusive (floats over the player, doesn't overlap the native transport controls) and matches the existing UI style.

Test Checklist

• Import a multi-dub HLS link and confirm the Audio language selector appears and lists 100+ languages.
• Switch from the default language to another (e.g. English → Spanish) and confirm the spoken audio changes and playback continues smoothly.
• Confirm the active language is shown/checked in the menu and persists while scrubbing/playing.
• Open a single-track video (plain MP4) and confirm the Audio language selector does not appear.
• Record or play a per-cell dub on top of the video; confirm it still mutes the video and plays correctly regardless of which audio-language track is selected.
• Toggle captions and audio language independently; confirm they don't interfere with each other.
• Switch audio language, then change cells/sections, and confirm the player and audio tracks stay in sync without errors.

[LeviXIII]

/build

[github-actions]

Pre-release: 0.29.0-pr1077-31381ca https://github.com/genesis-ai-dev/codex-editor/releases/tag/0.29.0-pr1077-31381ca