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/features/dialogue/dialogue_flow.dart

@@ -10,11 +10,26 @@ import '../../widgets/app_widgets.dart';
 import '../../widgets/lexicon_lookup.dart';
 
 class DialogueScenePage extends StatelessWidget {
-  const DialogueScenePage({super.key, required this.onStart});
+  const DialogueScenePage({
+    super.key,
+    required this.onStart,
+    this.onBack,
+  });
   final VoidCallback onStart;
+  final VoidCallback? onBack;
 
   @override
   Widget build(BuildContext context) => AppPage(
+    appBar: onBack != null
+        ? AppBar(
+            leading: IconButton(
+              icon: const Icon(Icons.arrow_back),
+              tooltip: "返回",
+              onPressed: onBack,
+            ),
+            title: const Text("AI 情境对话"),
+          )
+        : null,
     child: SpacedColumn(
       children: [
         const Eyebrow('按当前水平推荐'),
@@ -157,10 +172,17 @@ class _DialoguePageState extends State<DialoguePage> {
     } else {
       turns.add(DialogueTurn(text: script.prompts.first, isLearner: false));
     }
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (mounted) {
+        _playLatestAi(slow: false);
+      }
+    });
   }
 
   @override
   void dispose() {
+    VoiceService.instance.stopSpeaking();
+    VoiceService.instance.stopListening();
     VoiceService.instance.stopRecordingPlayback();
     if (!widget.state.keepRecordings) {
       VoiceService.instance.deleteRecording(recordingPath);
@@ -217,20 +239,21 @@ class _DialoguePageState extends State<DialoguePage> {
           .toList(),
     );
     if (!mounted) return;
+    final replyText = aiResponse?.reply ??
+        (nextStage < script.prompts.length
+            ? script.prompts[nextStage]
+            : 'Wonderful — nice meeting you!');
     setState(() {
       turns.add(
         DialogueTurn(
-          text:
-              aiResponse?.reply ??
-              (nextStage < script.prompts.length
-                  ? script.prompts[nextStage]
-                  : 'Wonderful — nice meeting you!'),
+          text: replyText,
           isLearner: false,
         ),
       );
       waitingForReply = false;
     });
     _saveDraft();
+    VoiceService.instance.speak(replyText);
   }
 
   void _saveDraft() {
@@ -417,6 +440,11 @@ class _DialoguePageState extends State<DialoguePage> {
     final finished = stage == script.prompts.length;
     return AppPage(
       appBar: AppBar(
+        leading: IconButton(
+          icon: const Icon(Icons.arrow_back),
+          tooltip: "返回",
+          onPressed: () => widget.onFinished(null),
+        ),
         title: Text(
           '${widget.isLessonDialogue ? '课程对话' : '初次见面'} · ${finished ? 4 : stage + 1} / 4',
         ),
@@ -446,7 +474,37 @@ class _DialoguePageState extends State<DialoguePage> {
                           : AppColors.softGreen,
                       borderRadius: BorderRadius.circular(15),
                     ),
-                    child: LexiconText(turn.text, state: widget.state),
+                    child: Column(
+                      crossAxisAlignment: CrossAxisAlignment.start,
+                      children: [
+                        LexiconText(turn.text, state: widget.state),
+                        if (!turn.isLearner) ...[
+                          const SizedBox(height: 6),
+                          GestureDetector(
+                            onTap: () => VoiceService.instance.speak(turn.text),
+                            child: const Row(
+                              mainAxisSize: MainAxisSize.min,
+                              children: [
+                                Icon(
+                                  Icons.volume_up_outlined,
+                                  size: 16,
+                                  color: AppColors.green,
+                                ),
+                                SizedBox(width: 4),
+                                Text(
+                                  "播放",
+                                  style: TextStyle(
+                                    fontSize: 12,
+                                    color: AppColors.green,
+                                    fontWeight: FontWeight.w500,
+                                  ),
+                                ),
+                              ],
+                            ),
+                          ),
+                        ],
+                      ],
+                    ),
                   ),
                 );
               },
@@ -612,13 +670,24 @@ class DialogueSummaryPage extends StatelessWidget {
     required this.onHome,
     required this.onLesson,
     required this.onRetry,
+    this.onBack,
   });
   final DialogueSummaryData summary;
   final VoidCallback onHome;
   final VoidCallback onLesson;
   final VoidCallback onRetry;
+  final VoidCallback? onBack;
+
   @override
   Widget build(BuildContext context) => AppPage(
+    appBar: AppBar(
+      leading: IconButton(
+        icon: const Icon(Icons.arrow_back),
+        tooltip: "返回",
+        onPressed: onBack ?? onHome,
+      ),
+      title: const Text("对话完成"),
+    ),
     child: SpacedColumn(
       children: [
         const Eyebrow('对话完成'),