fix(player): drop chapter-derived intro markers longer than three minutes

A movie whose first chapter is titled "Opening Credits" or "Introduction"
got a Skip Intro button that skipped the whole chapter — several minutes
of picture. Detected intros are short; only Plezy's own chapter-title
fallback produced these. Cap chapter-derived intros at three minutes.
Server-supplied markers and credits chapters are unaffected.

close #2235

lib/media/media_source_info.dart

@@ -376,11 +376,22 @@ class PlaybackExtras {
     return RegExp(source, caseSensitive: false);
   }
 
+  /// Longest chapter that may become a chapter-derived intro marker.
+  ///
+  /// Detected intros (Plex, Intro Skipper) fall well inside two minutes; a
+  /// movie's first chapter titled "Opening Credits" or "Introduction" runs
+  /// five to ten minutes of actual picture, and skipping it skips the film
+  /// (#2235). Applies only to markers minted here from chapter titles, never
+  /// to server-supplied markers, and never to credits, which are legitimately
+  /// long on movies.
+  static const maxChapterIntroDuration = Duration(minutes: 3);
+
   /// Returns [PlaybackExtras] using real markers when available, filling any
   /// missing marker types from chapter titles matching intro/credits patterns.
   /// [forceChapterFallback] prefers chapter-derived markers for any type they
   /// provide. When real markers exist, reclassifies markers with unknown types
   /// against the patterns so non-standard type strings get recognized.
+  /// Chapter-derived intros longer than [maxChapterIntroDuration] are dropped.
   factory PlaybackExtras.withChapterFallback({
     required List<MediaChapter> chapters,
     required List<MediaMarker> markers,
@@ -411,6 +422,7 @@ class PlaybackExtras {
 
       final end = ch.endTimeOffset ?? (i + 1 < chapters.length ? chapters[i + 1].startTimeOffset : null);
       if (end == null) continue;
+      if (type == 'intro' && end - start > maxChapterIntroDuration.inMilliseconds) continue;
 
       synthetic.add(MediaMarker(id: ch.id, type: type, startTimeOffset: start, endTimeOffset: end));
     }

test/media/media_source_info_test.dart

@@ -169,4 +169,85 @@ void main() {
       expect(extras.markers.single.startTimeOffset, 0);
     });
   });
+
+  group('PlaybackExtras.withChapterFallback intro duration cap', () {
+    const cap = PlaybackExtras.maxChapterIntroDuration;
+    const movieEnd = 7200000;
+
+    test('a movie-length "Opening Credits" chapter does not become an intro', () {
+      final extras = PlaybackExtras.withChapterFallback(
+        chapters: [
+          MediaChapter(id: 1, startTimeOffset: 0, endTimeOffset: 480000, title: 'Opening Credits'),
+          MediaChapter(id: 2, startTimeOffset: 480000, endTimeOffset: movieEnd, title: 'Chapter 2'),
+        ],
+        markers: [],
+      );
+
+      expect(extras.markers, isEmpty);
+    });
+
+    test('a chapter exactly at the cap still qualifies; one millisecond over does not', () {
+      final atCap = PlaybackExtras.withChapterFallback(
+        chapters: [
+          MediaChapter(id: 1, startTimeOffset: 1000, endTimeOffset: 1000 + cap.inMilliseconds, title: 'Intro'),
+        ],
+        markers: [],
+      );
+      final overCap = PlaybackExtras.withChapterFallback(
+        chapters: [
+          MediaChapter(id: 1, startTimeOffset: 1000, endTimeOffset: 1001 + cap.inMilliseconds, title: 'Intro'),
+        ],
+        markers: [],
+      );
+
+      expect(atCap.markers.map((m) => m.type), ['intro']);
+      expect(overCap.markers, isEmpty);
+    });
+
+    test('the cap uses the next chapter start when the chapter has no end', () {
+      final extras = PlaybackExtras.withChapterFallback(
+        chapters: [
+          MediaChapter(id: 1, startTimeOffset: 0, title: 'Opening'),
+          MediaChapter(id: 2, startTimeOffset: 600000, title: 'Chapter 2'),
+        ],
+        markers: [],
+      );
+
+      expect(extras.markers, isEmpty);
+    });
+
+    test('long credits chapters are still derived', () {
+      final extras = PlaybackExtras.withChapterFallback(
+        chapters: [
+          MediaChapter(id: 1, startTimeOffset: 0, endTimeOffset: 6600000, title: 'Chapter 1'),
+          MediaChapter(id: 2, startTimeOffset: 6600000, endTimeOffset: movieEnd, title: 'End Credits'),
+        ],
+        markers: [],
+      );
+
+      expect(extras.markers.map((m) => m.type), ['credits']);
+      expect(extras.markers.single.endTimeOffset, movieEnd);
+    });
+
+    test('server-supplied intro markers are never capped', () {
+      final extras = PlaybackExtras.withChapterFallback(
+        chapters: [],
+        markers: [MediaMarker(id: 1, type: 'intro', startTimeOffset: 0, endTimeOffset: 600000)],
+      );
+
+      expect(extras.markers.map((m) => m.type), ['intro']);
+      expect(extras.markers.single.endTimeOffset, 600000);
+    });
+
+    test('a dropped chapter intro leaves native markers intact under forced fallback', () {
+      final extras = PlaybackExtras.withChapterFallback(
+        chapters: [MediaChapter(id: 1, startTimeOffset: 0, endTimeOffset: 480000, title: 'Opening Credits')],
+        markers: [MediaMarker(id: 9, type: 'credits', startTimeOffset: 6600000, endTimeOffset: movieEnd)],
+        forceChapterFallback: true,
+      );
+
+      expect(extras.markers.map((m) => m.type), ['credits']);
+      expect(extras.markers.single.id, 9);
+    });
+  });
 }