feat(flutter): persist voice settings and per-user volume (TODO-039,040)

Add SharedPreferences persistence for transmit mode, release tail,
input/output device. Per-user volume/mute persisted across sessions.

apps/chanora_flutter/lib/widgets/voice_settings.dart

@@ -47,6 +47,8 @@ class VoiceSettingsDialog extends StatefulWidget {
     this.talkPower,
     this.neededTalkPower,
     this.talkPowerGranted,
+    this.onInputDeviceChanged,
+    this.onOutputDeviceChanged,
   });
 
   final rust.BridgeTransmitMode initialMode;
@@ -58,6 +60,8 @@ class VoiceSettingsDialog extends StatefulWidget {
   final int? talkPower;
   final int? neededTalkPower;
   final bool? talkPowerGranted;
+  final ValueChanged<String?>? onInputDeviceChanged;
+  final ValueChanged<String?>? onOutputDeviceChanged;
 
   @override
   State<VoiceSettingsDialog> createState() => _VoiceSettingsDialogState();
@@ -207,13 +211,15 @@ class _VoiceSettingsDialogState extends State<VoiceSettingsDialog> {
               if (!isAndroidHost && !isIosHost) ...[
                 const Divider(height: 24),
                 const VoiceSectionHeader('Audio devices'),
-                const AudioDeviceListTile(
+                AudioDeviceListTile(
                   label: 'Input',
                   kind: AudioDeviceKind.input,
+                  onDeviceChanged: widget.onInputDeviceChanged,
                 ),
-                const AudioDeviceListTile(
+                AudioDeviceListTile(
                   label: 'Output',
                   kind: AudioDeviceKind.output,
+                  onDeviceChanged: widget.onOutputDeviceChanged,
                 ),
                 const SizedBox(height: 8),
               ],