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/jellyfin/accounts.dart

@@ -23,6 +23,7 @@ const _keyDeviceId = 'deviceId';
 const _keyAccounts = 'accounts';
 const _keyDefault = 'defaultServer';
 const _keyLastPick = 'lastPick';
+const _keyBrowsePrefix = 'browse:';
 
 /// One signed-in user on one server.
 class JellyfinAccount {
@@ -124,10 +125,12 @@ abstract class JellyfinStore {
 }
 
 class HiveJellyfinStore implements JellyfinStore {
+  HiveJellyfinStore({this.boxName = jellyfinBoxName});
+  final String boxName;
   Box? _box;
 
   @override
-  Future<void> open() async => _box ??= await Hive.openBox(jellyfinBoxName);
+  Future<void> open() async => _box ??= await Hive.openBox(boxName);
 
   @override
   Object? get(String key) => _box?.get(key);
@@ -461,6 +464,26 @@ class JellyfinAccounts extends ChangeNotifier {
     }
   }
 
+  /// The browser's last location on [serverId] (encoded route stack, see
+  /// `browse_scope.dart`), restored by every browser and across restarts.
+  Object? browseLocation(String serverId) {
+    try {
+      final v = _store.get('$_keyBrowsePrefix$serverId');
+      return v is String ? _tryJson(v) : null;
+    } catch (_) {
+      return null;
+    }
+  }
+
+  Future<void> saveBrowseLocation(String serverId, Object? location) async {
+    try {
+      await _store.put(
+          '$_keyBrowsePrefix$serverId', location == null ? null : jsonEncode(location));
+    } catch (e) {
+      debugPrint('save browse location failed: $e');
+    }
+  }
+
   // --------------------------------------------------------------- cache
 
   /// Short-lived memo for browse calls, so going back does not refetch.