Restructure step 5: one media pipeline on a player host

- PlayerHost port (MediaKitHost): players by role, pins, hwdec policy,
  render probe, log routing, disposal order; the only media_kit user.
- MediaPipeline: plan (one pure switch over state, origin, caps,
  presence) -> resolve -> open (prepared player promoted, else fresh)
  -> ready; commands queued during a switch apply once (P15); viewers
  play the buffer and wait for a dropped source without seek loops (D6).
- Every web page resolved by our yt-dlp into an EDL with headers and
  cookies (danmaku excluded); mpv's ytdl_hook no longer used (ytdl=no).
- D11: sign-in errors say which cookies were used and whether they hold
  any for the site.
- Relay: 256 KiB slices read as they fill, superseded pulls released
  (seek-to-play ~4.2 s -> ~2.8 s, P29); own Jellyfin relay channel only
  when someone needs it (P28).
- STARSYNC_SMOKE run and a Windows CI smoke step after the build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/playback/yt_dlp_app.dart

@@ -6,15 +6,6 @@ import 'package:sync_relay_core/core.dart';
 
 import '../platform/ports/link_resolver.dart';
 
-/// mpv's `ytdl-format` for links every player opens itself.
-const ytdlFormat = 'bv*[height<=1080]+ba/b';
-
-/// yt-dlp's `--sub-langs` for mpv's hook (its default is `all`), without
-/// Bilibili's danmaku: an XML comment feed served raw-deflate, which
-/// ffmpeg fails to inflate on every read (a warning each time) while the
-/// video waits on it.
-const ytdlSubLangs = 'all,-danmaku';
-
 /// The app's yt-dlp (see [YtDlp]): in the app-support folder, shared with
 /// the hosted server. [probe] remembers what pasted links are for a while,
 /// so the Link preview and the swap ask once.
@@ -36,20 +27,10 @@ class AppYtDlp implements LinkResolver {
   /// Gets yt-dlp ready in the background (download on first run, a daily
   /// update check afterwards).
   @override
-  void warmUp() => unawaited(ytDlp.then((y) => y.ensure()).catchError((_) => null));
+  bool get resolvesLinks => true;
 
-  /// mpv's `ytdl-raw-options`: [ytdlSubLangs] and the cookies in the
-  /// yt-dlp folder (see [YtDlpCookies]).
   @override
-  Future<String> mpvRawOptions() async {
-    const subs = 'sub-langs=%${ytdlSubLangs.length}%$ytdlSubLangs';
-    try {
-      final cookies = (await ytDlp).cookies.mpvRawOptions();
-      return cookies.isEmpty ? subs : '$subs,$cookies';
-    } catch (_) {
-      return subs;
-    }
-  }
+  void warmUp() => unawaited(ytDlp.then((y) => y.ensure()).catchError((_) => null));
 
   final _probes = <String, ({DateTime at, DateTime until, Future<LinkProbe> f})>{};
   static const _probeTtl = Duration(minutes: 10);