修复大小写切换后新输入字母不跟随转换，输入时根据当前大小写状态存储

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

LearnEnglish/LearnEnglish/Views/QuizViewController.swift

@@ -218,6 +218,7 @@ final class QuizViewController: UIViewController {
 
         if isSpelling {
             spellingHintLabel.text = "\(question.word.word.count) 个字母，补全空缺部分"
+            spellingView.isUppercase = isUppercase
             spellingView.configure(blankedWord: question.blankedWord, blankPositions: question.blankPositions)
             if config.isStudyMode {
                 nextButton.isHidden = true
@@ -425,6 +426,7 @@ final class QuizViewController: UIViewController {
         isUppercase.toggle()
         UserDefaults.standard.set(isUppercase, forKey: "spelling_uppercase")
         updateCaseButton()
+        spellingView.isUppercase = isUppercase
         questions = QuizGenerator.recase(questions, toUpper: isUppercase)
         spellingView.updateCase(toUpper: isUppercase)
     }

LearnEnglish/LearnEnglish/Views/SpellingInputView.swift

@@ -17,6 +17,8 @@ final class SpellingInputView: UIView, UITextFieldDelegate {
     private var cursorView: UIView?
     private var inputEnabled = true
 
+    var isUppercase = false
+
     var isComplete: Bool {
         !filledBlanks.isEmpty && filledBlanks.allSatisfy { !$0.isEmpty }
     }
@@ -183,7 +185,8 @@ final class SpellingInputView: UIView, UITextFieldDelegate {
                 onChange?()
             }
         } else if let char = string.last, char.isLetter, cursorIndex < blankPositions.count {
-            filledBlanks[cursorIndex] = String(char).lowercased()
+            let converted = isUppercase ? char.uppercased() : char.lowercased()
+            filledBlanks[cursorIndex] = converted
             cursorIndex += 1
             refreshBoxes()
             popBox(atBlank: cursorIndex - 1)