Remove recognition history functionality

Complete removal of recognition history features:

1. State Variables Removed:
   - _recognitionHistory list variable
   - _realtimeResults list variable
   - All history-related state management

2. Methods Updated:
   - _clearHistory() renamed to _clearContent()
   - Simplified to only clear current text and base text
   - Removed history list operations

3. UI Components Removed:
   - _buildHistoryCard() method completely removed
   - History card from main layout removed
   - History-related ListView and ListTile widgets removed

4. Callback Logic Simplified:
   - onListeningStatusChanged callback cleaned up
   - Removed history insertion logic when recording stops
   - Removed _realtimeResults.clear() operations
   - Simplified state management to focus only on current text

5. App Bar Updated:
   - Clear button tooltip changed from '清除历史' to '清除内容'
   - Button now calls _clearContent() instead of _clearHistory()

The app now focuses purely on real-time speech recognition with
editable text input, without maintaining any recognition history.
This simplifies the codebase and improves performance by removing
unnecessary data storage and UI rendering.

example/lib/main.dart

@@ -40,14 +40,10 @@ class _SpeechRecognitionPageState extends State<SpeechRecognitionPage> {
   bool _isListening = false;
   String _currentText = '';
   String _errorMessage = '';
-  List<String> _recognitionHistory = [];
 
   /// 本次录音开始前的文本内容（用于实时追加）
   String _baseText = '';
 
-  // 录音相关
-  final List<String> _realtimeResults = []; // 存储实时识别片段
-
   @override
   void initState() {
     super.initState();
@@ -152,11 +148,9 @@ class _SpeechRecognitionPageState extends State<SpeechRecognitionPage> {
     );
   }
 
-  /// 清除历史记录
-  void _clearHistory() {
+  /// 清除内容
+  void _clearContent() {
     setState(() {
-      _recognitionHistory.clear();
-      _realtimeResults.clear();
       _currentText = '';
       _baseText = ''; // 也清空基础文本
       _textController.clear();
@@ -173,8 +167,8 @@ class _SpeechRecognitionPageState extends State<SpeechRecognitionPage> {
         actions: [
           IconButton(
             icon: const Icon(Icons.clear_all),
-            onPressed: _clearHistory,
-            tooltip: '清除历史',
+            onPressed: _clearContent,
+            tooltip: '清除内容',
           ),
         ],
       ),
@@ -189,9 +183,6 @@ class _SpeechRecognitionPageState extends State<SpeechRecognitionPage> {
             // 识别结果卡片
             _buildRecognitionCard(),
             const SizedBox(height: 16),
-
-            // 历史记录
-            Expanded(child: _buildHistoryCard()),
           ],
         ),
       ),
@@ -396,66 +387,6 @@ class _SpeechRecognitionPageState extends State<SpeechRecognitionPage> {
     );
   }
 
-  /// 构建历史记录卡片
-  Widget _buildHistoryCard() {
-    return Card(
-      child: Padding(
-        padding: const EdgeInsets.all(16.0),
-        child: Column(
-          crossAxisAlignment: CrossAxisAlignment.start,
-          children: [
-            const Text(
-              '识别历史',
-              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
-            ),
-            const SizedBox(height: 16),
-            Expanded(
-              child: _recognitionHistory.isEmpty
-                  ? Center(
-                      child: Text(
-                        '暂无识别历史',
-                        style: TextStyle(
-                          color: Colors.grey[600],
-                          fontStyle: FontStyle.italic,
-                        ),
-                      ),
-                    )
-                  : ListView.builder(
-                      itemCount: _recognitionHistory.length,
-                      itemBuilder: (context, index) {
-                        return Card(
-                          margin: const EdgeInsets.only(bottom: 8.0),
-                          child: ListTile(
-                            leading: CircleAvatar(
-                              backgroundColor: Theme.of(context).primaryColor,
-                              child: Text(
-                                '${index + 1}',
-                                style: const TextStyle(color: Colors.white),
-                              ),
-                            ),
-                            title: Text(_recognitionHistory[index]),
-                            trailing: IconButton(
-                              icon: const Icon(Icons.copy),
-                              onPressed: () {
-                                // TODO: 实现复制到剪贴板功能
-                                ScaffoldMessenger.of(context).showSnackBar(
-                                  const SnackBar(
-                                    content: Text('已复制到剪贴板'),
-                                  ),
-                                );
-                              },
-                            ),
-                          ),
-                        );
-                      },
-                    ),
-            ),
-          ],
-        ),
-      ),
-    );
-  }
-
   /// 构建浮动操作按钮
   Widget _buildFloatingActionButton() {
     if (!_isInitialized) {
@@ -508,16 +439,6 @@ class _SpeechRecognitionPageState extends State<SpeechRecognitionPage> {
         });
 
         if (!isListening) {
-          // 录音结束后，确认当前文本并保存到历史记录
-          if (_currentText.isNotEmpty) {
-            setState(() {
-              _recognitionHistory.insert(0, _currentText);
-              // 限制历史记录数量
-              if (_recognitionHistory.length > 10) {
-                _recognitionHistory.removeLast();
-              }
-            });
-          }
           // 录音结束后，更新基础文本为下次录音做准备
           setState(() {
             _baseText = _textController.text; // 保存当前文本作为下次的基础
@@ -527,7 +448,6 @@ class _SpeechRecognitionPageState extends State<SpeechRecognitionPage> {
           // 开始录音时记录当前文本作为基础，清空当前识别文本
           setState(() {
             _baseText = _textController.text; // 记录录音开始前的文本
-            _realtimeResults.clear();
             _currentText = ''; // 清空当前识别文本
           });
         }