refactor(player): delete the webview video path; mpv selects its own tracks

DR-235 phase 3. Every video renderer is native now: mpv on Linux and
Windows, ExoPlayer on Android, all drawing behind the transparent
webview. The HTML5 <video> path is gone, not bypassed:

- Frontend: hls.js, Html5PlayerAdapter and its compatibility shim, the
  createAdapter factory, streamTransport, hlsRecovery, timeTracking,
  videoFit, the <video>/<track> markup and every element handler in
  VideoPlayer (3277 -> 2144 lines), the experimentalNativeVideo store
  and its Settings toggle, webviewVideoFallback/supportsNativeVideo, and
  the setHtml5VideoState PiP bridge call. NativePlayerAdapter is the one
  video adapter; webview audio gets its own adapter kind.
- Rust: use_html5 dropped from player_seek_video,
  player_switch_audio_track and player_set_stream_quality with the
  Html5* strategies and ReloadStream responses; use_html5_element and
  VideoBackend dropped from PlayerStatus; player_play_item always loads
  the backend (set_current_item removed); Capabilities::webview removed;
  the WebKitGTK GStreamer/VAAPI setup (and its gst-inspect spawn) removed.
- Android: the HTML5 video state in PictureInPictureManager and
  ScreenWakeManager, and the bridge method feeding it.
- CSP: connect-src loses http:/https: and worker-src loses blob: -
  both existed for hls.js; with it gone they were only an exfiltration
  channel and a blob worker for injected script. A test now keeps them
  out.

mpv takes over what the <video> element did (mpv_tracks, UT-275):
subtitles are the WebVTT list the play request carries, queued on
sub-files and selected by position in that list, starting off; audio
tracks are selected by position in the file; sid/aid are reset before
each load. Without this, Linux video had no subtitle selection and a
direct-play audio switch failed since mpv became its renderer.

Verified: Rust 948 passing, and the same 948 cross-compiled for Windows
under wine against the shipped DLL (track tests included); frontend
1111 passing; aarch64 debug APK builds. Lint warnings 158 -> 146, CI
ratchet tightened to match. Not yet seen on Windows hardware.

docs/architecture/README.md

@@ -99,7 +99,7 @@ Each major subsystem is documented in its own file in this directory:
 | [02 - Svelte Frontend](02-svelte-frontend.md) | Store structure, music library navigation, playback reporting, repository architecture, playback mode system, database service abstraction, component hierarchy, MiniPlayer, sleep timer, auto-play, navigation guard, playlist management UI, library mosaic, series/episode navigation, downloaded browse, safe-area insets, native-video store, logging |
 | [03 - Data Flow](03-data-flow.md) | Repository query flow (cache-first), locally-indexed search, playback initiation, playback mode transfer, queue navigation, volume control |
 | [04 - Type Sync & Threading](04-type-sync-and-threading.md) | Rust/TypeScript type synchronization, Tauri v2 IPC parameter naming convention, thread safety patterns |
-| [05 - Platform Backends](05-platform-backends.md) | Player events system, HTML5 video adapter, MpvBackend (Linux), ExoPlayerBackend (Android) incl. audio settings parity, **native video compositing**, MediaSession & remote volume, album art caching, backend initialization |
+| [05 - Platform Backends](05-platform-backends.md) | Player events system, MpvBackend (Linux), ExoPlayerBackend (Android) incl. audio settings parity, **native video compositing**, MediaSession & remote volume, album art caching, backend initialization |
 | [06 - Downloads & Offline](06-downloads-and-offline.md) | Download manager, download worker, smart caching engine, **one storage model (cache entries are downloads)**, offline catalog visibility, download/offline commands, player integration, frontend store, UI components |
 | [07 - Connectivity](07-connectivity.md) | HTTP client with retry logic, connectivity monitor, network resilience architecture |
 | [08 - Database Design](08-database-design.md) | Entity relationships, all table definitions (servers, users, libraries, items, user_data, downloads, media_streams, sync_queue, thumbnails, playlists), key queries, data flow diagrams, storage estimates |
@@ -176,7 +176,6 @@ src/lib/
 │   └── sessions.ts          # SessionsApi (remote session control)
 ├── player/                  # Unified player boundary (frontend)
 │   ├── index.ts             # playerController facade — the only write-side entry point for playback
-│   └── html5Adapter.ts      # Reports webview <video> DOM events back into Rust (player_report_*)
 ├── services/
 │   ├── playerEvents.ts      # Tauri event listener for player events
 │   └── playbackReporting.ts # Thin wrapper (~50 lines)