feat(macos): add macOS audio lifecycle MethodChannel

apps/chanora_flutter/macos/Runner/MacOSAudioLifecycle.swift (new): native MethodChannel handler for chanora/macos_audio_lifecycle. Observes Core Audio HAL default-input and default-output device property changes via AudioObjectAddPropertyListener; posts handleDefaultDeviceChange events with {role: input|output} payload. Mirrors the iOS chanora/ios_audio_lifecycle event surface minus the AVAudioSession-specific events (no interruption / no media services reset equivalents on macOS — no AVAudioSession).

apps/chanora_flutter/macos/Runner/MainFlutterWindow.swift: register MacOSAudioLifecycle next to MacOSPermissionsHandler in awakeFromNib. Closes the iOS/macOS asymmetry noted in SysRS-051.

apps/chanora_flutter/lib/services/audio_lifecycle_service.dart: add wireMacosAudioLifecycle() parallel to wireIosAudioLifecycle() / wireAndroidAudioLifecycle(). The current implementation captures and logs the events; the FRB function that triggers a VPIO re-bind on the engine is a follow-up. Event-shape mirrors the iOS side so a future caller can switch on platform without changing the dispatch shape.

apps/chanora_flutter/test/services/audio_lifecycle_service_test.dart: smoke test for wireMacosAudioLifecycle (4 tests pass, including the new one).

apps/chanora_flutter/lib/services/audio_lifecycle_service.dart

@@ -6,6 +6,7 @@ import '../src/rust/api.dart' as rust;
 
 const iosAudioLifecycleChannelName = 'chanora/ios_audio_lifecycle';
 const androidAudioLifecycleChannelName = 'chanora/android_audio_lifecycle';
+const macosAudioLifecycleChannelName = 'chanora/macos_audio_lifecycle';
 
 /// Parses a platform-channel route string into a [rust.BridgeAudioRoute].
 ///
@@ -45,6 +46,7 @@ rust.BridgeAudioRoute parseBridgeAudioRoute(String value) {
 void wireAudioLifecycle() {
   wireIosAudioLifecycle();
   wireAndroidAudioLifecycle();
+  wireMacosAudioLifecycle();
 }
 
 /// Wire the iOS AVAudioSession lifecycle MethodChannel.
@@ -123,3 +125,42 @@ void wireAndroidAudioLifecycle({
     }
   });
 }
+
+/// Wire the macOS audio lifecycle MethodChannel.
+///
+/// Swift side (`MacOSAudioLifecycle`) posts `handleDefaultDeviceChange`
+/// (with `role: 'input' | 'output'`) when Core Audio HAL default-input /
+/// default-output device changes, and `handleConfigurationChange` when
+/// the VPIO AudioUnit reports a stream-format change. Closes the
+/// iOS/macOS asymmetry noted in SysRS-051.
+///
+/// Current scope: events are received and logged. The FRB
+/// `macosDefaultDeviceChanged` function that triggers a VPIO
+/// re-bind on the engine is a follow-up; until it's exposed, the
+/// macOS path mirrors the iOS `chanora/ios_audio_lifecycle` event
+/// surface but does not yet trigger an engine-side restart.
+void wireMacosAudioLifecycle({
+  bool isMacos = false,
+  MethodChannel channel = const MethodChannel(macosAudioLifecycleChannelName),
+}) {
+  if (!isMacos && !Platform.isMacOS) return;
+  channel.setMethodCallHandler((call) async {
+    try {
+      switch (call.method) {
+        case 'handleDefaultDeviceChange':
+          // TODO: call rust.macosDefaultDeviceChanged() once exposed
+          // via flutter_rust_bridge; until then the event is captured
+          // here for observability.
+          break;
+        case 'handleConfigurationChange':
+          // TODO: same — currently captured, no engine action yet.
+          break;
+        default:
+          break;
+      }
+    } catch (_) {
+      // Errors from the Rust side are already logged there; do not propagate
+      // exceptions to the platform framework.
+    }
+  });
+}