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/09-security.md

@@ -68,8 +68,8 @@ style-src   'self' 'unsafe-inline';
 font-src    'self' data:;
 img-src     'self' data: blob: asset: http://asset.localhost http: https:;
 media-src   'self' blob: asset: http://asset.localhost http://127.0.0.1:* http: https:;
-connect-src 'self' ipc: http://ipc.localhost http: https:;
-worker-src  'self' blob:;
+connect-src 'self' ipc: http://ipc.localhost;
+worker-src  'self';
 object-src 'none'; frame-src 'none'; base-uri 'self'; form-action 'self'; frame-ancestors 'none'
 ```
 
@@ -79,13 +79,13 @@ object-src 'none'; frame-src 'none'; base-uri 'self'; form-action 'self'; frame-
 | `script-src 'self'` | The genuinely restrictive half. Bundled JS only; Tauri's build-time nonce covers the one inline `<script>` in `index.html`. Adding `'unsafe-inline'` here would silently do nothing anyway — a nonce in a directive voids it. |
 | `style-src 'self' 'unsafe-inline'` | Svelte compiles `style="…"` attributes into markup, including `app.html`'s `display: contents` wrapper, and CSP treats a style *attribute* as inline. Safe only while no `<style>` **element** survives into `index.html`: Tauri would nonce it, and the nonce would then void `'unsafe-inline'`. The production build extracts all CSS to files, so it currently has none. |
 | `img-src` | Thumbnails come from two places: the asset protocol (`asset://localhost/…` on Linux/macOS, `http://asset.localhost/…` on Windows/Android — the same protocol, named differently by `convertFileSrc`) and, on a cache miss, straight from the Jellyfin server. `data:`/`blob:` cover inline and generated images. |
-| `media-src` | `<video>`/`<audio>` sources: HLS transcodes and progressive streams from the server, the token-guarded loopback media server on `http://127.0.0.1:<random port>` (DR-137), and `blob:` for the MSE object URL hls.js attaches. |
-| `connect-src` | `ipc:` / `http://ipc.localhost` is Tauri's `invoke` transport (custom scheme on Linux/macOS, `http` host on Windows/Android) — without it every command is blocked. `http:`/`https:` is hls.js fetching manifests and segments; ordinary API traffic goes through Rust and is not subject to CSP. |
-| `worker-src 'self' blob:` | hls.js runs its demuxer in a worker built from a blob (`enableWorker: true`). Without `blob:` it falls back to main-thread demuxing — playback survives but costs more CPU. |
+| `media-src` | `<audio>` sources for the webview audio backend (a desktop without mpv; no shipped platform): streams from the server and the token-guarded loopback media server on `http://127.0.0.1:<random port>` (DR-137). Video never plays in the webview (DR-235). |
+| `connect-src` | `ipc:` / `http://ipc.localhost` is Tauri's `invoke` transport (custom scheme on Linux/macOS, `http` host on Windows/Android) — without it every command is blocked. Nothing else: all network traffic goes through Rust. It allowed any `http:`/`https:` host while hls.js fetched manifests and segments in the page; with hls.js gone (DR-235) that grant was only an exfiltration channel for injected script, so it went too. |
+| `worker-src 'self'` | No blob workers since hls.js (whose demuxer ran in one) was removed (DR-235). |
 | `object-src`, `frame-src` = `'none'` | No plugins, no iframes; both are classic injection sinks. |
 | `base-uri 'self'`, `form-action 'self'`, `frame-ancestors 'none'` | Block `<base>` hijacking, form exfiltration and framing. `frame-ancestors` is only honoured when the policy is delivered as a header, which is platform-dependent; it is harmless where it is not. |
 
-**`img-src`/`media-src`/`connect-src` are deliberately permissive.** The Jellyfin
+**`img-src`/`media-src` are deliberately permissive.** The Jellyfin
 origin is typed in by the user at run time and is routinely plain `http` on a
 LAN, so it cannot be enumerated at build time. `http: https:` is a wide grant for
 *data* — but it still bars `file:`, `filesystem:` and scripting schemes, and it