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/progress/progress_pages.dart

@@ -199,8 +199,10 @@ class _AbilityRow extends StatelessWidget {
 }
 
 class SettingsPage extends StatefulWidget {
-  const SettingsPage({super.key, required this.state});
+  const SettingsPage({super.key, required this.state, this.onBack});
   final AppState state;
+  final VoidCallback? onBack;
+
   @override
   State<SettingsPage> createState() => _SettingsPageState();
 }
@@ -209,6 +211,8 @@ class _SettingsPageState extends State<SettingsPage> {
   late final TextEditingController endpoint;
   late final TextEditingController model;
   final apiKey = TextEditingController();
+  bool _testingConnection = false;
+
   @override
   void initState() {
     super.initState();
@@ -226,7 +230,20 @@ class _SettingsPageState extends State<SettingsPage> {
 
   @override
   Widget build(BuildContext context) => AppPage(
-    appBar: AppBar(title: const Text('学习设置')),
+    appBar: AppBar(
+      leading: IconButton(
+        icon: const Icon(Icons.arrow_back),
+        tooltip: "返回",
+        onPressed: () {
+          if (widget.onBack != null) {
+            widget.onBack!();
+          } else if (Navigator.canPop(context)) {
+            Navigator.pop(context);
+          }
+        },
+      ),
+      title: const Text('学习设置'),
+    ),
     child: SpacedColumn(
       spacing: 4,
       children: [
@@ -350,17 +367,49 @@ class _SettingsPageState extends State<SettingsPage> {
           },
         ),
         SecondaryButton(
-          label: '测试连接',
+          label: _testingConnection ? '正在测试连接...' : '测试连接',
+          onPressed: _testingConnection
+              ? null
+              : () async {
+                  setState(() => _testingConnection = true);
+                  final result = await AiService.instance.testConnection(
+                    provider: widget.state.aiProvider,
+                    endpoint: endpoint.text,
+                    model: model.text,
+                    explicitApiKey: apiKey.text,
+                  );
+                  if (!mounted) return;
+                  setState(() => _testingConnection = false);
+                  ScaffoldMessenger.of(context).showSnackBar(
+                    SnackBar(
+                      content: Text(result.message),
+                      backgroundColor:
+                          result.ok ? AppColors.green : Colors.redAccent,
+                      duration: const Duration(seconds: 4),
+                    ),
+                  );
+                },
+        ),
+        SecondaryButton(
+          label: '从配置文件重载 (ai_config.json)',
           onPressed: () async {
-            final result = await AiService.instance.testConnection(
-              provider: widget.state.aiProvider,
-              endpoint: endpoint.text,
-              model: model.text,
-            );
-            if (!context.mounted) return;
-            ScaffoldMessenger.of(
-              context,
-            ).showSnackBar(SnackBar(content: Text(result.message)));
+            final ok = await widget.state.reloadAiConfigFromAsset();
+            if (!mounted) return;
+            if (ok) {
+              setState(() {
+                endpoint.text = widget.state.aiEndpoint;
+                model.text = widget.state.aiModel;
+              });
+              ScaffoldMessenger.of(context).showSnackBar(
+                const SnackBar(
+                  content: Text('已从 assets/config/ai_config.json 载入配置。'),
+                ),
+              );
+            } else {
+              ScaffoldMessenger.of(context).showSnackBar(
+                const SnackBar(content: Text('未找到配置文件或解析失败。')),
+              );
+            }
           },
         ),
         const Divider(height: 28),