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/widgets/lexicon_lookup.dart

@@ -21,10 +21,20 @@ List<VocabularyItem> get courseLexiconEntries {
 
 /// Finds a course item by exact query, then by the longest known phrase in it.
 VocabularyItem? findCourseLexicon(String text) {
-  final normalized = text.toLowerCase().replaceAll('’', "'").trim();
+  final normalized = text
+      .toLowerCase()
+      .replaceAll('’', "'")
+      .replaceAll('‘', "'")
+      .replaceAll(RegExp(r'\s+'), ' ')
+      .trim();
   if (normalized.isEmpty) return null;
   return courseLexiconEntries.cast<VocabularyItem?>().firstWhere((entry) {
-    final word = entry!.word.toLowerCase().replaceAll('’', "'");
+    final word = entry!.word
+        .toLowerCase()
+        .replaceAll('’', "'")
+        .replaceAll('‘', "'")
+        .replaceAll(RegExp(r'\s+'), ' ')
+        .trim();
     if (normalized == word) return true;
     final pattern = RegExp(
       r'(?<![a-zA-Z0-9])' + RegExp.escape(word) + r'(?![a-zA-Z0-9])',
@@ -36,12 +46,22 @@ VocabularyItem? findCourseLexicon(String text) {
 
 /// Extracts all distinct course lexicon phrases/words that appear within [text].
 List<VocabularyItem> extractCourseLexiconPhrases(String text) {
-  final normalized = text.toLowerCase().replaceAll('’', "'").trim();
+  final normalized = text
+      .toLowerCase()
+      .replaceAll('’', "'")
+      .replaceAll('‘', "'")
+      .replaceAll(RegExp(r'\s+'), ' ')
+      .trim();
   if (normalized.isEmpty) return const [];
   final matched = <VocabularyItem>[];
   final seen = <String>{};
   for (final item in courseLexiconEntries) {
-    final word = item.word.toLowerCase().replaceAll('’', "'");
+    final word = item.word
+        .toLowerCase()
+        .replaceAll('’', "'")
+        .replaceAll('‘', "'")
+        .replaceAll(RegExp(r'\s+'), ' ')
+        .trim();
     if (word.isEmpty || word == normalized) continue;
     final pattern = RegExp(
       r'(?<![a-zA-Z0-9])' + RegExp.escape(word) + r'(?![a-zA-Z0-9])',