fix: 修正学习流程中的证据、复习与进度问题

- 独立尝试按课程要求校验内容，不再任意输入即算独立成功
- 复习节点改为学后第 1/3/7/14 天，之后每 30 天抽查；复习轮换情境
- 掌握状态按作答记录推导：需认识、可回忆、跨情境使用及最近两次无帮助
- 课程证据按实际用到的目标记录；跟读与课程对话只算辅助练习
- 复习成功不再降低已有状态
- 学完课程后进入下一节未完成课程；全部学完后引导巩固与阶段评估
- 新增 3 题基础定位，按结果设置起始课程
- 新增按课程开放的对话场景，首页推荐最少练习的场景
- 切换课程时清空上一课的步骤进度
- AI 返回 JSON 格式并按 JSON 回放历史；拼写校验忽略大小写与连字符；移除学习目标选择

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

kouyu_english/lib/core/review_feedback.dart

@@ -1,3 +1,4 @@
+import 'a0_core.dart';
 import 'models.dart';
 
 class ReviewCheckResult {
@@ -21,70 +22,20 @@ class ReviewFeedback {
       .trim();
 
   static ReviewCheckResult check(ReviewItem item, String input) {
-    final text = _normalize(input);
-    final tokens = RegExp(
-      r"[a-z]+(?:'[a-z]+)?",
-    ).allMatches(text).map((match) => match.group(0)!).toSet();
-    bool has(String token) => tokens.contains(_normalize(token));
-    bool phrase(String value) => text.contains(_normalize(value));
-    bool hasAny(Iterable<String> values) => values.any(has);
-    final introduction =
-        phrase("i'm") || phrase('i am') || phrase('my name is');
-    final itIs = phrase("it's") || phrase('it is');
-    final numberWords = RegExp(
-      r'\b(zero|one|two|three|four|five|six|seven|eight|nine|ten)\b',
-    ).allMatches(text).length;
-
-    final complete = switch (item.id) {
-      'A0-P01' => introduction && tokens.length >= 2,
-      'A0-P02' => (phrase("what's your name") || phrase('what is your name')),
-      'A0-P03' => phrase('nice to meet you'),
-      'A0-P04' => phrase('how do you spell'),
-      'A0-P05' => phrase('how are you'),
-      'A0-P06' => introduction && hasAny(['good', 'okay', 'tired']),
-      'A0-P07' =>
-        phrase("what's your phone number") ||
-            phrase('what is your phone number'),
-      'A0-P08' =>
-        (phrase('my number is') || numberWords >= 3) && numberWords >= 3,
-      'A0-P09' => phrase("what's this") || phrase('what is this'),
-      'A0-P10' => itIs && hasAny(['book', 'pen', 'bag', 'key']),
-      'A0-P11' => phrase('where are you from'),
-      'A0-P12' => introduction && has('from') && tokens.length >= 3,
-      'A0-P13' => phrase('this is my') && tokens.length >= 4,
-      'A0-P14' => phrase('what day is it'),
-      'A0-P15' =>
-        itIs &&
-            hasAny([
-              'monday',
-              'tuesday',
-              'wednesday',
-              'thursday',
-              'friday',
-              'saturday',
-              'sunday',
-            ]),
-      'A0-P16' => phrase('what time is it'),
-      'A0-P17' =>
-        itIs &&
-            (has('clock') ||
-                has("o'clock") ||
-                has('oclock') ||
-                phrase("o'clock")),
-      'A0-P18' => introduction && has('like') && tokens.length >= 3,
-      'A0-P19' => phrase('do you like'),
-      'A0-P20' =>
-        phrase('please say that again') || phrase('please speak slowly'),
-      _ when item.id.startsWith('A0-W') =>
-        tokens.contains(_normalize(item.target)) || phrase(item.target),
-      _ => tokens.length >= 2,
-    };
+    final complete = a0CoreItems.containsKey(item.id)
+        // A word review checks the word it actually shows.
+        ? coreItemUsedIn(item.id, input, word: item.target)
+        : _tokens(_normalize(input)).length >= 2;
     return ReviewCheckResult(
       complete: complete,
       message: complete ? '表达已完成，可以进入下一次复习安排。' : _hint(item.id),
     );
   }
 
+  static Set<String> _tokens(String text) => RegExp(
+    r"[a-z]+(?:'[a-z]+)?",
+  ).allMatches(text).map((match) => match.group(0)!).toSet();
+
   static String _hint(String id) => switch (id) {
     'A0-P01' => '用 I’m / I am 或 My name is 介绍一个名字。',
     'A0-P02' => '试着问：What’s your name?',
@@ -97,3 +48,66 @@ class ReviewFeedback {
     _ => '再补充本次目标中的关键英文词或句型。',
   };
 }
+
+/// Whether [input] actually contains A0 core item [id]. Lessons, reviews and
+/// dialogues use the same rule, so evidence only goes to the items a learner
+/// really produced, never to every target a task happens to be attached to.
+bool coreItemUsedIn(String id, String input, {String? word}) {
+  final text = ReviewFeedback._normalize(input);
+  final tokens = ReviewFeedback._tokens(text);
+  bool has(String token) => tokens.contains(ReviewFeedback._normalize(token));
+  bool phrase(String value) => text.contains(ReviewFeedback._normalize(value));
+  bool hasAny(Iterable<String> values) => values.any(has);
+  final introduction = phrase("i'm") || phrase('i am') || phrase('my name is');
+  final itIs = phrase("it's") || phrase('it is');
+  final numberWords = RegExp(
+    r'\b(zero|one|two|three|four|five|six|seven|eight|nine|ten)\b',
+  ).allMatches(text).length;
+  const weekdays = [
+    'monday',
+    'tuesday',
+    'wednesday',
+    'thursday',
+    'friday',
+    'saturday',
+    'sunday',
+  ];
+
+  return switch (id) {
+    // "I'm from …" and "I'm good" are other items, not a name.
+    'A0-P01' =>
+      phrase('my name is') ||
+          RegExp(
+            r"\bi(?:'m| am) (?!from\b|good\b|okay\b|ok\b|fine\b|great\b|tired\b)[a-z]",
+          ).hasMatch(text),
+    'A0-P02' => phrase("what's your name") || phrase('what is your name'),
+    'A0-P03' => phrase('nice to meet you'),
+    'A0-P04' => phrase('how do you spell'),
+    'A0-P05' => phrase('how are you'),
+    'A0-P06' => introduction && hasAny(['good', 'okay', 'tired']),
+    'A0-P07' =>
+      phrase("what's your phone number") || phrase('what is your phone number'),
+    'A0-P08' => numberWords >= 3,
+    'A0-P09' => phrase("what's this") || phrase('what is this'),
+    'A0-P10' => itIs && hasAny(['book', 'pen', 'bag', 'key', 'phone']),
+    'A0-P11' => phrase('where are you from'),
+    'A0-P12' => introduction && has('from') && tokens.length >= 3,
+    'A0-P13' => phrase('this is my') && tokens.length >= 4,
+    'A0-P14' => phrase('what day is it'),
+    'A0-P15' => itIs && hasAny(weekdays),
+    'A0-P16' => phrase('what time is it'),
+    'A0-P17' =>
+      itIs &&
+          (has('clock') ||
+              has("o'clock") ||
+              has('oclock') ||
+              phrase("o'clock")),
+    'A0-P18' => introduction && has('like') && tokens.length >= 3,
+    'A0-P19' => phrase('do you like'),
+    'A0-P20' =>
+      phrase('please say that again') || phrase('please speak slowly'),
+    _ when a0CoreItems.containsKey(id) && id.startsWith('A0-W') =>
+      has(word ?? a0CoreItems[id]!) || phrase(word ?? a0CoreItems[id]!),
+    _ => false,
+  };
+}