Chapters on the scrubber, Skip OP/ED, audio/subtitle menus

- PlaybackController exposes chapters, segments (Jellyfin
  MediaSegments for account holders), tracks, position/duration.
- Own seek bar with chapter diamonds and chapter title on hover,
  seeking through the sync user-seek path.
- Skip OP / Skip ED pills from Intro/Outro segments or chapter names
  (ED skips to its end only); Skip 1:30 fallback for >20 min videos
  without OP info; next-episode pill now starts at the ED.
- PgUp/PgDn chapters, Shift+Right +1:30; Audio and Subtitles menus
  with count badges via the existing track path.

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

packages/core/lib/src/jellyfin/client.dart

@@ -499,6 +499,27 @@ class JellyfinClient {
   Map<String, String> get authHeaders =>
       {'Authorization': clientInfo.authorizationHeader(accessToken)};
 
+  /// `GET /MediaSegments/{itemId}` (Jellyfin 10.10+): the item's intro,
+  /// outro, recap, preview and commercial ranges, in start order. Empty when
+  /// no segment provider has marked it, and on servers without the
+  /// endpoint (404).
+  Future<List<JellyfinMediaSegment>> mediaSegments(String itemId) async {
+    final Object? j;
+    try {
+      j = await _json('GET', '/MediaSegments/$itemId');
+    } on JellyfinException catch (e) {
+      if (e.statusCode == 404) return const [];
+      rethrow;
+    }
+    final items = _map(j)['Items'];
+    final list = [
+      if (items is List)
+        for (final e in items)
+          if (e is Map) JellyfinMediaSegment.fromJson(e.cast<String, dynamic>())
+    ]..sort((a, b) => a.startTicks.compareTo(b.startTicks));
+    return list;
+  }
+
   // ------------------------------------------------------------ progress
 
   /// `POST /Sessions/Playing`: playback started (Jellyfin shows the session

packages/core/lib/src/jellyfin/models.dart

@@ -555,3 +555,54 @@ class JellyfinPlaybackInfo {
     return mediaSources.isEmpty ? null : mediaSources.first;
   }
 }
+
+/// Kind of a [JellyfinMediaSegment] (Jellyfin `MediaSegmentType`).
+enum JellyfinSegmentType {
+  unknown,
+  commercial,
+  preview,
+  recap,
+  outro,
+  intro;
+
+  static JellyfinSegmentType parse(String? v) => switch (v) {
+        'Commercial' => commercial,
+        'Preview' => preview,
+        'Recap' => recap,
+        'Outro' => outro,
+        'Intro' => intro,
+        _ => unknown,
+      };
+}
+
+/// A marked range of an item (`GET /MediaSegments/{itemId}`, Jellyfin
+/// 10.10+): intro, outro, recap, preview or commercial. Filled by segment
+/// provider plugins; without one the list is empty.
+class JellyfinMediaSegment {
+  final String id;
+  final String itemId;
+  final JellyfinSegmentType type;
+  final int startTicks;
+  final int endTicks;
+  const JellyfinMediaSegment({
+    required this.id,
+    required this.itemId,
+    required this.type,
+    required this.startTicks,
+    required this.endTicks,
+  });
+
+  Duration get start => ticksToDuration(startTicks);
+  Duration get end => ticksToDuration(endTicks);
+
+  factory JellyfinMediaSegment.fromJson(JellyfinJson j) => JellyfinMediaSegment(
+        id: _str(j['Id']) ?? '',
+        itemId: _str(j['ItemId']) ?? '',
+        type: JellyfinSegmentType.parse(_str(j['Type'])),
+        startTicks: _int(j['StartTicks']) ?? 0,
+        endTicks: _int(j['EndTicks']) ?? 0,
+      );
+
+  @override
+  String toString() => 'JellyfinMediaSegment(${type.name} $start-$end)';
+}