fix: 输入校验忽略多个连续空格与大小写；统一中英文引号与空白规范化

kouyu_english/lib/core/writing_feedback.dart

@@ -11,18 +11,25 @@ class WritingCheckResult {
 class WritingFeedback {
   const WritingFeedback._();
 
+  static String _normalize(String input) => input
+      .toLowerCase()
+      .replaceAll('’', "'")
+      .replaceAll('‘', "'")
+      .replaceAll(RegExp(r'\s+'), ' ')
+      .trim();
+
   static WritingCheckResult check(
     String lessonId,
     String input, {
     String? segmentId,
   }) {
-    final text = input.toLowerCase().replaceAll('’', "'");
+    final text = _normalize(input);
     final words = RegExp(
       r"[a-z]+(?:'[a-z]+)?",
     ).allMatches(text).map((match) => match.group(0)!).toSet();
-    bool has(String word) => words.contains(word);
+    bool has(String word) => words.contains(_normalize(word));
 
-    bool hasPhrase(String phrase) => text.contains(phrase);
+    bool hasPhrase(String phrase) => text.contains(_normalize(phrase));
 
     bool hasAny(Iterable<String> choices) => choices.any(has);
     final hasIntroduction =
@@ -40,7 +47,7 @@ class WritingFeedback {
       'a0-08-a' => hasItIs && hasAny(['monday', 'tuesday', 'wednesday']),
       'a0-08-b' =>
         hasItIs && hasAny(['thursday', 'friday', 'saturday', 'sunday']),
-      'a0-08-c' => hasItIs && (has('oclock') || text.contains("o'clock")),
+      'a0-08-c' => hasItIs && (has('oclock') || hasPhrase("o'clock")),
       _ => switch (lessonId) {
         'a0-01' => hasAny(['hello', 'hi']) && hasIntroduction,
         'a0-02' =>