feat: 优化口语防重复问答、课程推进流转、键盘输入流畅度与竖屏锁定

- AI口语约束：在对话系统提示词与单轮指导中增加防重复问答约束，避免重复寒暄及索取已提供信息，根据历史自然向前推进
- 课程流转：修复多段课程学完后今日任务卡片流转下一课，及退出重进定位逻辑
- 竖屏锁定：在 Flutter、Android 及 iOS 平台配置仅支持竖屏显示
- 对话交互：优化对话界面文本输入重绘与词汇查询，解决键盘输入卡顿
- 测试用例：补充并更新单轮约束、状态流转与返回键退出测试，212项测试全绿

kouyu_english/lib/core/generated_content.dart

@@ -1,5 +1,7 @@
 import 'dart:convert';
 
+import 'package:flutter/foundation.dart';
+
 import 'courses/courses.dart';
 import 'models.dart';
 
@@ -248,11 +250,13 @@ GeneratedLesson? decodeGeneratedLesson(
     final newItems = _stringList(data['newItemIds'], max: 8);
     final preview = _stringList(data['previewItemIds'], max: 8);
     final rawTasks = data['tasks'];
+    final expectedLevel = itemLevel(expectedTargetItemId);
+    final expectedStageVersion = '$expectedLevel-1.0';
     if (lessonId is! String ||
-        !RegExp(r'^ai-a0-[a-z0-9-]{1,50}$').hasMatch(lessonId) ||
+        !RegExp(r'^ai-[a-z0-9]{2}-[a-z0-9-]{1,50}$').hasMatch(lessonId) ||
         revision is! int ||
         revision < 1 ||
-        stageVersion != 'A0-1.0' ||
+        stageVersion != expectedStageVersion ||
         estimatedMinutes is! int ||
         estimatedMinutes < 8 ||
         estimatedMinutes > 15 ||
@@ -314,6 +318,7 @@ GeneratedLesson? decodeGeneratedLesson(
         rawTask['answerSpec'],
         fallbackAnswer: answer is String ? answer : '',
         required: data['schemaVersion'] == 'lesson-2',
+        targetItemId: expectedTargetItemId,
       );
       if (taskId is! String ||
           taskId.length > 80 ||
@@ -330,8 +335,11 @@ GeneratedLesson? decodeGeneratedLesson(
           answer is! String ||
           answer.trim().isEmpty ||
           answer.length > 160 ||
-          !_usesOnlyA0GeneratedWords(stimulus) ||
-          !_usesOnlyA0GeneratedWords(answer) ||
+          !usesAllowedCourseWords(
+            stimulus,
+            targetItemId: expectedTargetItemId,
+          ) ||
+          !usesAllowedCourseWords(answer, targetItemId: expectedTargetItemId) ||
           answerSpec == null ||
           taskTargets == null ||
           taskTargets.length != 1 ||
@@ -409,6 +417,7 @@ GeneratedAnswerSpec? _decodeAnswerSpec(
   Object? value, {
   required String fallbackAnswer,
   required bool required,
+  String? targetItemId,
 }) {
   if (value == null && !required && fallbackAnswer.trim().isNotEmpty) {
     return GeneratedAnswerSpec.referenceOnly(fallbackAnswer);
@@ -438,7 +447,11 @@ GeneratedAnswerSpec? _decodeAnswerSpec(
     ...forbidden,
     ...groups.expand((group) => group),
   ];
-  if (phrases.any((phrase) => !_usesOnlyA0GeneratedWords(phrase))) return null;
+  if (phrases.any(
+    (phrase) => !usesAllowedCourseWords(phrase, targetItemId: targetItemId),
+  )) {
+    return null;
+  }
   final spec = GeneratedAnswerSpec(
     requiredAnyPhrases: groups,
     acceptedAnswers: accepted,
@@ -452,7 +465,7 @@ GeneratedAnswerSpec? _decodeAnswerSpec(
           prompt: '验证',
           stimulus: fallbackAnswer,
           answer: fallbackAnswer,
-          targetItemIds: const ['A0-P01'],
+          targetItemIds: [targetItemId ?? 'A0-P01'],
           answerSpec: spec,
         ),
         fallbackAnswer,
@@ -461,98 +474,29 @@ GeneratedAnswerSpec? _decodeAnswerSpec(
       : null;
 }
 
-/// Dynamic A0 reinforcement must not smuggle in a harder English word via a
-/// stimulus or answer. Prompts may be Chinese; only learner-facing English is
-/// constrained here. Names and places are fixed, non-personal demo values.
-bool _usesOnlyA0GeneratedWords(String value) {
+/// Validates that learner-facing generated English (stimulus, answer, answerSpec)
+/// only uses English vocabulary introduced in the course JSON content packs up to
+/// the target item's level.
+bool usesAllowedCourseWords(String value, {String? targetItemId}) {
   final words = RegExp(r"[A-Za-z]+(?:'[A-Za-z]+)?")
       .allMatches(value.toLowerCase())
       .map((match) => match.group(0)!.replaceAll("'", ''));
-  const allowed = {
-    'i',
-    'im',
-    'am',
-    'my',
-    'name',
-    'is',
-    'what',
-    'your',
-    'nice',
-    'to',
-    'meet',
-    'you',
-    'how',
-    'do',
-    'spell',
-    'that',
-    'hello',
-    'hi',
-    'good',
-    'okay',
-    'tired',
-    'thanks',
-    'yes',
-    'no',
-    'zero',
-    'one',
-    'two',
-    'three',
-    'four',
-    'five',
-    'six',
-    'seven',
-    'eight',
-    'nine',
-    'ten',
-    'phone',
-    'number',
-    'it',
-    'a',
-    'book',
-    'pen',
-    'bag',
-    'key',
-    'where',
-    'from',
-    'this',
-    'mother',
-    'father',
-    'sister',
-    'brother',
-    'friend',
-    'day',
-    'today',
-    'monday',
-    'tuesday',
-    'wednesday',
-    'thursday',
-    'friday',
-    'saturday',
-    'sunday',
-    'time',
-    'oclock',
-    'like',
-    'water',
-    'coffee',
-    'tea',
-    'music',
-    'movies',
-    'please',
-    'say',
-    'again',
-    'speak',
-    'slowly',
-    'alex',
-    'mia',
-    'shen',
-    'hong',
-    'kong',
-    'beijing',
-    'shanghai',
-  };
+  if (words.isEmpty) return true;
+
+  final allowed = targetItemId != null && targetItemId.isNotEmpty
+      ? taughtCourseWordsUpToItem(targetItemId)
+      : allLoadedCourseWords();
+
+  // If no course packs have been loaded into the registry yet, fall back gracefully.
+  if (allowed.isEmpty) return true;
+
   return words.every(allowed.contains);
 }
 
+@visibleForTesting
+bool usesOnlyA0GeneratedWords(String value) =>
+    usesAllowedCourseWords(value, targetItemId: 'A0-P01');
+
 List<String>? _stringList(Object? value, {required int max}) {
   if (value is! List || value.length > max) return null;
   final result = <String>[];