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/generated_content.dart

@@ -122,6 +122,8 @@ bool matchesAdaptiveLessonAnswer(GeneratedLessonTask task, String answer) {
 
 String _normalizeAnswer(String value) => value
     .toLowerCase()
+    .replaceAll('’', "'")
+    .replaceAll('‘', "'")
     .replaceAll(RegExp(r"[^a-z0-9']+"), ' ')
     .trim()
     .replaceAll(RegExp(r'\s+'), ' ');