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- Relay: 256 KiB slices read as they fill, superseded pulls released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/controls/model/controls_model.dart

@@ -121,7 +121,7 @@ class PlayerControlsModel {
 
   /// A seek bar's press or drag; through `player.seek`, the user-seek
   /// path, so everyone follows.
-  void seek(Duration to) => playback.player.seek(to);
+  void seek(Duration to) => playback.userSeek(to);
 
   /// Arrow keys: ±[secs], relative to a seek still in flight.
   void nudge(double secs) => coord.nudge(secs);
@@ -157,7 +157,7 @@ class PlayerControlsModel {
 
   void playNextEpisode() => coord.playNextEpisode();
 
-  void setVolume(double v) => playback.player.setVolume(v.clamp(0.0, vol.maxVolume));
+  void setVolume(double v) => playback.setVolume(v.clamp(0.0, vol.maxVolume));
 
   /// One volume step up (+1) or down (-1) from the wheel or ↑ / ↓;
   /// flashes the volume readout.

apps/desktop/lib/src/controls/player_settings.dart

@@ -222,7 +222,9 @@ class ShaderPresetSetting extends StatelessWidget {
       final preset = s.shaderPreset.value;
       final quality = s.shaderQuality.value;
       final hasCustom = s.customShaders.value.isNotEmpty;
-      final mode = (renderMode ?? PlaybackController.lastRenderMode).value;
+      final mode = (renderMode ??
+              context.getInheritedWidgetOfExactType<AppScope>()?.graph.ports.players.renderMode)
+          ?.value;
       final warning = switch (mode) {
         RenderMode.software => 'Software rendering: shaders have no effect',
         RenderMode.softwareGl => 'OpenGL on the CPU: shaders will be slow',
@@ -267,10 +269,10 @@ class ShaderPresetSetting extends StatelessWidget {
 /// on the fly). `SYNC_RELAY_HWDEC` wins, as at player start.
 Future<void> applyHwdecLive(PlaybackController playback) async {
   if ((Platform.environment['SYNC_RELAY_HWDEC'] ?? '').isNotEmpty) return;
-  if (!playback.alive.peek()) return;
+  final p = playback.current;
+  if (p == null) return;
   try {
-    final dynamic platform = playback.player.platform;
-    await platform?.setProperty('hwdec', AppSettings.instance.hwdec.peek());
+    await p.setProperty('hwdec', AppSettings.instance.hwdec.peek());
   } catch (e) {
     debugPrint('live hwdec failed: $e');
   }