feat(voice): pulse mic button with live amplitude

VoiceState now carries a normalized mic amplitude (0..1) updated
from the existing onAmplitudeChanged subscription, with a 0.02
change threshold so we don't spam rebuilds.

VoiceMicButton swaps the constant-rate AnimationController for an
AnimatedScale + animated glow driven by the live amplitude. 0.1
floor keeps the button breathing on silence; 120ms ease-out smooths
between 200ms samples.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/widgets/voice_mic_button.dart

@@ -5,51 +5,29 @@ import '../providers/voice_provider.dart';
 /// Animated mic button that reflects the current [VoiceMode].
 ///
 /// - idle: muted background, mic_none icon
-/// - recording: red with pulsing shadow ring
+/// - recording: red, pulses with live [amplitude] for real-time feedback
 /// - transcribing: indigo with spinner
 /// - playing: indigo with volume_up icon
-class VoiceMicButton extends StatefulWidget {
+class VoiceMicButton extends StatelessWidget {
   final VoiceMode mode;
   final bool voiceModeActive;
+  /// Live mic amplitude 0.0–1.0 while recording. Drives the button scale
+  /// and glow so the user has obvious feedback that audio is being picked
+  /// up. Ignored when not in [VoiceMode.recording].
+  final double amplitude;
   final VoidCallback? onTap;
 
   const VoiceMicButton({
     super.key,
     required this.mode,
     required this.voiceModeActive,
+    this.amplitude = 0.0,
     this.onTap,
   });
 
-  @override
-  State<VoiceMicButton> createState() => _VoiceMicButtonState();
-}
-
-class _VoiceMicButtonState extends State<VoiceMicButton>
-    with SingleTickerProviderStateMixin {
-  late AnimationController _pulseController;
-  late Animation<double> _pulseAnimation;
-
-  @override
-  void initState() {
-    super.initState();
-    _pulseController = AnimationController(
-      vsync: this,
-      duration: const Duration(milliseconds: 900),
-    )..repeat(reverse: true);
-    _pulseAnimation = Tween<double>(begin: 1.0, end: 1.25).animate(
-      CurvedAnimation(parent: _pulseController, curve: Curves.easeInOut),
-    );
-  }
-
-  @override
-  void dispose() {
-    _pulseController.dispose();
-    super.dispose();
-  }
-
   Color _bgColor(BuildContext context) {
     final cs = Theme.of(context).colorScheme;
-    return switch (widget.mode) {
+    return switch (mode) {
       VoiceMode.recording => const Color(0xFFEF4444),
       VoiceMode.transcribing || VoiceMode.playing => cs.primary,
       VoiceMode.idle => cs.surfaceContainerHighest,
@@ -58,11 +36,10 @@ class _VoiceMicButtonState extends State<VoiceMicButton>
 
   Widget _icon(BuildContext context) {
     final cs = Theme.of(context).colorScheme;
-    final iconColor = widget.mode == VoiceMode.idle
-        ? cs.onSurfaceVariant
-        : Colors.white;
+    final iconColor =
+        mode == VoiceMode.idle ? cs.onSurfaceVariant : Colors.white;
 
-    return switch (widget.mode) {
+    return switch (mode) {
       VoiceMode.transcribing => SizedBox(
           width: 18,
           height: 18,
@@ -78,14 +55,14 @@ class _VoiceMicButtonState extends State<VoiceMicButton>
 
   @override
   Widget build(BuildContext context) {
-    final isRecording = widget.mode == VoiceMode.recording;
+    final isRecording = mode == VoiceMode.recording;
 
     final button = Material(
       color: _bgColor(context),
       shape: const CircleBorder(),
       child: InkWell(
         customBorder: const CircleBorder(),
-        onTap: widget.onTap,
+        onTap: onTap,
         child: SizedBox(
           width: 40,
           height: 40,
@@ -96,22 +73,30 @@ class _VoiceMicButtonState extends State<VoiceMicButton>
 
     if (!isRecording) return button;
 
-    return AnimatedBuilder(
-      animation: _pulseAnimation,
-      builder: (_, child) => Container(
-        decoration: BoxDecoration(
-          shape: BoxShape.circle,
-          boxShadow: [
-            BoxShadow(
-              color: const Color(0xFFEF4444).withValues(alpha: 0.35),
-              blurRadius: 8 * _pulseAnimation.value,
-              spreadRadius: 2 * _pulseAnimation.value,
-            ),
-          ],
-        ),
-        child: child,
+    // Base pulse so silence still breathes (0.1 floor), scale + glow climb
+    // linearly with live amplitude.
+    final amp = amplitude.clamp(0.0, 1.0);
+    final pulse = 0.1 + amp * 0.9;
+
+    return AnimatedContainer(
+      duration: const Duration(milliseconds: 120),
+      curve: Curves.easeOut,
+      decoration: BoxDecoration(
+        shape: BoxShape.circle,
+        boxShadow: [
+          BoxShadow(
+            color: const Color(0xFFEF4444).withValues(alpha: 0.2 + pulse * 0.3),
+            blurRadius: 6 + pulse * 14,
+            spreadRadius: 1 + pulse * 5,
+          ),
+        ],
+      ),
+      child: AnimatedScale(
+        scale: 1.0 + pulse * 0.18,
+        duration: const Duration(milliseconds: 120),
+        curve: Curves.easeOut,
+        child: button,
       ),
-      child: button,
     );
   }
 }