feat: 增加AI配置文件与TTS自动朗读，修复二级页面返回按钮与音频播放

kouyu_english/lib/core/voice_service.dart

@@ -17,15 +17,53 @@ class VoiceService {
   final AudioRecorder _recorder = AudioRecorder();
   final AudioPlayer _player = AudioPlayer();
   bool _speechReady = false;
+  bool _ttsInitialized = false;
 
-  Future<void> speak(String text, {bool slow = false}) async {
-    await _tts.stop();
-    await _tts.setLanguage('en-US');
-    await _tts.setSpeechRate(slow ? 0.35 : 0.48);
-    await _tts.speak(text);
+  Future<void> _initTts() async {
+    if (_ttsInitialized) return;
+    try {
+      if (Platform.isIOS) {
+        await _tts.setIosAudioCategory(
+          IosTextToSpeechAudioCategory.playback,
+          [
+            IosTextToSpeechAudioCategoryOptions.allowBluetooth,
+            IosTextToSpeechAudioCategoryOptions.allowBluetoothA2DP,
+            IosTextToSpeechAudioCategoryOptions.mixWithOthers,
+          ],
+        );
+      }
+      await _tts.setVolume(1.0);
+      await _tts.setPitch(1.0);
+      _ttsInitialized = true;
+    } catch (_) {}
   }
 
-  Future<void> stopSpeaking() => _tts.stop();
+  Future<void> speak(String text, {bool slow = false}) async {
+    try {
+      await _initTts();
+      await _tts.stop();
+      try {
+        final isAvailable = await _tts.isLanguageAvailable('en-US');
+        if (isAvailable == true) {
+          await _tts.setLanguage('en-US');
+        } else {
+          await _tts.setLanguage('en');
+        }
+      } catch (_) {
+        try {
+          await _tts.setLanguage('en-US');
+        } catch (_) {}
+      }
+      await _tts.setSpeechRate(slow ? 0.35 : 0.48);
+      await _tts.speak(text);
+    } catch (_) {}
+  }
+
+  Future<void> stopSpeaking() async {
+    try {
+      await _tts.stop();
+    } catch (_) {}
+  }
 
   Future<bool> startRecording() async {
     if (!await _recorder.hasPermission()) return false;