Update RecordingButton design to match UI mockup

Design improvements based on provided mockup:

1. Color Updates:
   - Idle state: Blue (#2196F3) - matches mockup's blue recording button
   - Recording state: Red (#FF5252) - matches mockup's red stop button
   - Disabled state: Light grey (#9E9E9E) for better visibility
   - Processing state: Semi-transparent versions of respective colors

2. Shape Changes:
   - Idle state: Circle (for recording button)
   - Recording state: Rounded rectangle (12px radius) for stop button
   - Smooth transitions between shapes using BoxShape

3. Icon Improvements:
   - Use rounded icons (mic_rounded, stop_rounded) for modern look
   - Adjust icon sizes: recording (40% of button), stop (35% of button)
   - Better proportions matching the design intent

4. Shadow Enhancements:
   - Increased blur radius for idle state (8→12px) for better depth
   - Dynamic shadow based on button state
   - Enhanced spread radius for better visual impact

5. Interactive Elements:
   - InkWell borderRadius adapts to button shape
   - Smooth transitions between circular and rectangular ripple effects

These changes create a modern, professional appearance that matches
common design patterns and provides clear visual feedback for different states.

lib/src/widgets/recording_button.dart

@@ -168,7 +168,8 @@ class _RecordingButtonState extends State<RecordingButton>
       if (_isListening) {
         await _speechService.stopListening();
       } else {
-        await _speechService.startListening(partialResults: widget.partialResults);
+        await _speechService.startListening(
+            partialResults: widget.partialResults);
       }
     } catch (e) {
       widget.onError?.call(SpeechRecognitionError(
@@ -190,17 +191,19 @@ class _RecordingButtonState extends State<RecordingButton>
 
   @override
   Widget build(BuildContext context) {
-    final theme = Theme.of(context);
-    
     Color buttonColor;
     if (!widget.enabled || !_isInitialized) {
-      buttonColor = widget.disabledColor ?? Colors.grey;
+      buttonColor = widget.disabledColor ?? Colors.grey[400]!;
     } else if (_isProcessing) {
-      buttonColor = (widget.idleColor ?? theme.primaryColor).withValues(alpha: 0.7);
+      buttonColor = _isListening
+          ? (widget.recordingColor ?? const Color(0xFFFF5252))
+              .withValues(alpha: 0.7)
+          : (widget.idleColor ?? const Color(0xFF2196F3))
+              .withValues(alpha: 0.7);
     } else if (_isListening) {
-      buttonColor = widget.recordingColor ?? Colors.red;
+      buttonColor = widget.recordingColor ?? const Color(0xFFFF5252); // 红色停止按钮
     } else {
-      buttonColor = widget.idleColor ?? theme.primaryColor;
+      buttonColor = widget.idleColor ?? const Color(0xFF2196F3); // 蓝色录音按钮
     }
 
     Widget button = AnimatedBuilder(
@@ -213,12 +216,13 @@ class _RecordingButtonState extends State<RecordingButton>
             height: widget.size,
             decoration: BoxDecoration(
               color: buttonColor,
-              shape: BoxShape.circle,
+              shape: _isListening ? BoxShape.rectangle : BoxShape.circle,
+              borderRadius: _isListening ? BorderRadius.circular(12) : null,
               boxShadow: [
                 BoxShadow(
                   color: buttonColor.withValues(alpha: 0.3),
-                  blurRadius: _isListening ? 20 : 8,
+                  blurRadius: _isListening ? 20 : 12,
-                  spreadRadius: _isListening ? 5 : 2,
+                  spreadRadius: _isListening ? 5 : 3,
                 ),
               ],
             ),
@@ -233,12 +237,13 @@ class _RecordingButtonState extends State<RecordingButton>
                         height: widget.size * 0.4,
                         child: CircularProgressIndicator(
                           strokeWidth: 2,
-                          valueColor: AlwaysStoppedAnimation<Color>(Colors.white),
+                          valueColor:
+                              AlwaysStoppedAnimation<Color>(Colors.white),
                         ),
                       )
                     : Icon(
-                        _isListening ? Icons.stop : Icons.mic,
+                        _isListening ? Icons.stop_rounded : Icons.mic_rounded,
-                        size: widget.size * 0.4,
+                        size: widget.size * (_isListening ? 0.35 : 0.4),
                         color: Colors.white,
                       ),
               ),