feat: configurable intro/credits marker regex patterns

Add settings to customize regex patterns for matching intro and credits
markers in chapter titles, with the current hardcoded values as defaults.
Also reclassifies real markers with non-standard type strings against the
configured patterns.

lib/services/settings_service.dart

@@ -57,6 +57,13 @@ class SettingsService extends BaseSharedPreferencesService {
   static const String _keyAutoSkipIntro = 'auto_skip_intro';
   static const String _keyAutoSkipCredits = 'auto_skip_credits';
   static const String _keyAutoSkipDelay = 'auto_skip_delay';
+  static const String _keyIntroPattern = 'intro_pattern';
+  static const String _keyCreditsPattern = 'credits_pattern';
+
+  static const String defaultIntroPattern =
+      r'(?:^|\b)(?:intro(?:duction)?|opening)(?:\b|$)|^op(?:\s?\d+)?$';
+  static const String defaultCreditsPattern =
+      r'(?:^|\b)(?:outro|closing|credits?|ending)(?:\b|$)|^ed(?:\s?\d+)?$';
   static const String _keyCustomDownloadPath = 'custom_download_path';
   static const String _keyCustomDownloadPathType = 'custom_download_path_type';
   static const String _keyDownloadOnWifiOnly = 'download_on_wifi_only';
@@ -894,6 +901,24 @@ class SettingsService extends BaseSharedPreferencesService {
     return prefs.getInt(_keyAutoSkipDelay) ?? 5; // Default: 5 seconds
   }
 
+  // Intro Pattern
+  Future<void> setIntroPattern(String value) async {
+    await prefs.setString(_keyIntroPattern, value);
+  }
+
+  String getIntroPattern() {
+    return prefs.getString(_keyIntroPattern) ?? defaultIntroPattern;
+  }
+
+  // Credits Pattern
+  Future<void> setCreditsPattern(String value) async {
+    await prefs.setString(_keyCreditsPattern, value);
+  }
+
+  String getCreditsPattern() {
+    return prefs.getString(_keyCreditsPattern) ?? defaultCreditsPattern;
+  }
+
   // Custom Download Path
   Future<void> setCustomDownloadPath(String? path, {String type = 'file'}) async {
     if (path == null) {
@@ -1381,6 +1406,8 @@ class SettingsService extends BaseSharedPreferencesService {
       'autoSkipIntro': getAutoSkipIntro(),
       'autoSkipCredits': getAutoSkipCredits(),
       'autoSkipDelay': getAutoSkipDelay(),
+      'introPattern': getIntroPattern(),
+      'creditsPattern': getCreditsPattern(),
     };
   }
 }