Jellyfin end to end: per-viewer playback, progress, episodes, swap browser

- Host/swap send refs only; pasted Jellyfin links become refs; the host
  hands the relay its own app-obtained credential.
- Each viewer resolves with their own account (token in a header) or
  via the relay, else a clear blocked card with Link account.
- Per-account progress reporting (Playing/Progress/Stopped), 401 marks
  the account expired.
- Previous/next episode in the controls (< > / Shift+P/N), floating
  Next episode pill near the end, auto-advance countdown (one
  designated swapper), track carry-over per series.
- Swap panel uses the shared MediaPicker; browser location remembered
  per server and opens on the current series.
- Fix: states are applied one at a time (a stale pause could land
  after a newer play).

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

apps/desktop/lib/src/state/settings.dart

@@ -16,6 +16,7 @@ const _keyAutoCheckUpdates = 'autoCheckUpdates';
 const _keyShaderPreset = 'shaderPreset';
 const _keyShaderQuality = 'shaderQuality';
 const _keyCustomShaders = 'customShaders';
+const _keyAutoAdvance = 'autoAdvance';
 
 enum HwdecMode { auto, off, custom }
 
@@ -25,6 +26,8 @@ class AppSettings {
   final hwdecMode = signal(HwdecMode.auto);
   final hwdecCustom = signal('');
   final autoCheckUpdates = signal(true);
+  /// Jellyfin episodes: at the end, count down 10 s and put up the next.
+  final autoAdvance = signal(true);
 
   /// Video shaders: one choice, used on join and changed both here and
   /// in the session (Ctrl+0..6, the shader button).
@@ -59,6 +62,8 @@ class AppSettings {
       if (custom is String) hwdecCustom.value = custom;
       final auto = box.get(_keyAutoCheckUpdates);
       if (auto is bool) autoCheckUpdates.value = auto;
+      final advance = box.get(_keyAutoAdvance);
+      if (advance is bool) autoAdvance.value = advance;
       final preset = box.get(_keyShaderPreset);
       shaderPreset.value =
           ShaderPreset.values.where((p) => p.name == preset).firstOrNull ??
@@ -91,6 +96,11 @@ class AppSettings {
     _put(_keyAutoCheckUpdates, on);
   }
 
+  void setAutoAdvance(bool on) {
+    autoAdvance.value = on;
+    _put(_keyAutoAdvance, on);
+  }
+
   void setShaderPreset(ShaderPreset preset) {
     shaderPreset.value = preset;
     _put(_keyShaderPreset, preset.name);