fix: stabilize player and collection flows

[Priveetee]

Summary

• show managed allow-list users and prevent allow-list layout overflow
• fix iOS downloader artifact opening and watch history clear behavior
• use collection metadata directly for favorites, watch later, and playlists
• add subscribed channel listing with the subscriptions videos/channels switch
• add the watch history tracking privacy toggle
• stabilize Vidstack runtime behavior, reduce player signal churn, and add playlist previous/next controls

Production behavior

• admins can inspect managed allow-list users without overflowing the allow-list UI
• iOS Safari opens downloader artifacts through the browser share/open flow instead of doing nothing
• clearing watch history updates cached UI state and failures are surfaced
• imported collection videos render from backend metadata without stream enrichment
• Subscriptions can show followed channels separately from subscription videos
• users can disable watch history and playback progress tracking from Settings > Privacy
• playlist watch playback supports previous/next controls and Media Session track actions
• mobile keeps the existing player control layout; fullscreen mobile repositioning is not included
• refs Feature Request: Allow List Mode for Channels and Content #112, [Feature]: List of subscripted channels #115, [Bug]: Download share sheet does nothing on iOS Safari (works on desktop) #116, [Bug]: Watch history not clearing and UI inconsistencies across desktop and mobile #117, [Bug]: Importing YouTube takeout playlist shows blank information for all videos #118, [Feature]: Option to disable watch history and playback progress tracking #119, [Feature]: Player UI improvements, next/previous buttons and fullscreen repositioning #120

Deployment requirements

• deploy the matching TypeType-Server collection metadata contract before or with this frontend update
• backend settings must preserve the disableWatchHistory field
• no new frontend dependencies are added

Runtime verification

• beta collection metadata behavior was verified after the backend contract updates
• player runtime was smoke-tested against playlist playback without the Vidstack picture-in-picture null-target crash
• player warning filtering remains scoped to the Vidstack development update-depth stack only

Tests

• bun run --cwd apps/web tsc -b --force
• bun run check
• bun run knip
• bun run build
• git diff --check

Rollback

• revert the collection metadata commits if imported collection rows regress
• revert the subscription channel listing commit if subscriptions navigation regresses
• revert the history tracking toggle commit if settings persistence regresses
• revert the Vidstack runtime and track navigation commits if playback controls regress