feat: 重做阅读找答案题与 AI 情境对话，并归拢本地识别、查词等既有改动

阅读"在对话里找到答案"：
- 16 道题全部重写，干扰项真实出现在对话里，靠说话人归属或否定句才能作答
- 选项按题目内容确定性打乱，答案不再固定排第一；听力环节同样处理
- 去掉超纲干扰项、重复题干，收紧自由作答匹配（过去单个字母也能判对）

AI 情境对话：
- 提示词区分"AI 这一句要做什么"与"学习者随后要完成什么"，并下发已教词句清单
- JSON 只强制 reply，translation/feedback 可选；不再索要用不上的 slots/evidence
- AI 不可用时页面明确提示当前回复来自内置示范脚本
- 删掉按 stage 下标猜中文翻译的兜底，避免译文与英文对不上
- 整课对话改用逐轮必需表达校验，替换"关键词沾边就算过"；修正自由场景正则误伤
- 总结的"完成任务"按实际通过的轮次生成；模型点评只在结束页呈现一次
- 自由场景支持草稿续练（独立存储槽）；修正回答轮数文案与永不解锁的场景标注

同时提交此前工作区中累积的改动：SenseVoice 本地识别、查词/句型解析卡、
复习与测评页调整等，并补充对话校验、选项分布和句子解析的测试。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kouyu_english/lib/features/progress/progress_pages.dart

@@ -6,6 +6,7 @@ import '../../core/ai_service.dart';
 import '../../core/app_theme.dart';
 import '../../core/models.dart';
 import '../../core/voice_service.dart';
+import '../../core/sherpa_stt_service.dart';
 import '../../widgets/app_widgets.dart';
 import '../../core/sync/sync_coordinator.dart';
 import 'sync_settings_sheet.dart';
@@ -321,6 +322,22 @@ class _SettingsPageState extends State<SettingsPage> {
           onTap: () => _confirmDeleteRecordings(context),
         ),
         const Divider(height: 28),
+        const Text(
+          '离线语音识别引擎',
+          style: TextStyle(fontSize: 16, fontWeight: FontWeight.w600),
+        ),
+        const Text(
+          '已内置 SenseVoice-Small 高精度离线语音识别模型 (INT8)。随 App 安装包直接打包，离线即用，无需额外下载，零网络流量消耗。',
+          style: TextStyle(fontSize: 12, color: AppColors.muted),
+        ),
+        _SettingTile(
+          title: '离线语音识别：SenseVoice-Small',
+          subtitle: SherpaSttService.instance.isReady
+              ? '已就绪 · 本地离线识别 (16kHz WAV · INT8)'
+              : '预加载就绪 · 已内置打包',
+          trailing: const Icon(Icons.check_circle, color: AppColors.green, size: 20),
+        ),
+        const Divider(height: 28),
         const Text(
           '云同步与多端备份',
           style: TextStyle(fontSize: 16, fontWeight: FontWeight.w600),
@@ -351,7 +368,7 @@ class _SettingsPageState extends State<SettingsPage> {
           style: TextStyle(fontSize: 12, color: AppColors.muted),
         ),
         DropdownButtonFormField<AiProviderType>(
-          value: widget.state.aiProvider,
+          initialValue: widget.state.aiProvider,
           decoration: const InputDecoration(
             labelText: '服务类型',
             border: OutlineInputBorder(),
@@ -436,6 +453,7 @@ class _SettingsPageState extends State<SettingsPage> {
           onPressed: _testingConnection
               ? null
               : () async {
+                  final messenger = ScaffoldMessenger.of(context);
                   setState(() => _testingConnection = true);
                   final result = await AiService.instance.testConnection(
                     provider: widget.state.aiProvider,
@@ -445,7 +463,7 @@ class _SettingsPageState extends State<SettingsPage> {
                   );
                   if (!mounted) return;
                   setState(() => _testingConnection = false);
-                  ScaffoldMessenger.of(context).showSnackBar(
+                  messenger.showSnackBar(
                     SnackBar(
                       content: Text(result.message),
                       backgroundColor:
@@ -458,6 +476,7 @@ class _SettingsPageState extends State<SettingsPage> {
         SecondaryButton(
           label: '从配置文件重载 (ai_config.json)',
           onPressed: () async {
+            final messenger = ScaffoldMessenger.of(context);
             final ok = await widget.state.reloadAiConfigFromAsset();
             if (!mounted) return;
             if (ok) {
@@ -465,13 +484,13 @@ class _SettingsPageState extends State<SettingsPage> {
                 endpoint.text = widget.state.aiEndpoint;
                 model.text = widget.state.aiModel;
               });
-              ScaffoldMessenger.of(context).showSnackBar(
+              messenger.showSnackBar(
                 const SnackBar(
                   content: Text('已从 assets/config/ai_config.json 载入配置。'),
                 ),
               );
             } else {
-              ScaffoldMessenger.of(context).showSnackBar(
+              messenger.showSnackBar(
                 const SnackBar(content: Text('未找到配置文件或解析失败。')),
               );
             }
@@ -608,17 +627,20 @@ class _SettingTile extends StatelessWidget {
   const _SettingTile({
     required this.title,
     required this.subtitle,
-    required this.onTap,
+    this.onTap,
+    this.trailing,
   });
   final String title;
   final String subtitle;
   final VoidCallback? onTap;
+  final Widget? trailing;
+
   @override
   Widget build(BuildContext context) => ListTile(
     contentPadding: const EdgeInsets.symmetric(horizontal: 4),
     title: Text(title),
     subtitle: Text(subtitle),
-    trailing: const Icon(Icons.chevron_right),
+    trailing: trailing ?? (onTap != null ? const Icon(Icons.chevron_right) : null),
     onTap: onTap,
   );
 }