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/test/services/audio_lifecycle_service_test.dart

@@ -39,5 +39,17 @@ void main() {
     // than misclassify as Speaker.
     expect(parseBridgeAudioRoute('Hdmi'), rust.BridgeAudioRoute.unknown);
   });
+
+  test('wireMacosAudioLifecycle is a no-op on non-macOS and registers on macOS', () {
+    // MethodChannel needs a binary messenger, which requires the test
+    // binding to be initialised first.
+    TestWidgetsFlutterBinding.ensureInitialized();
+    // Channel name constant matches the Swift side (MacOSAudioLifecycle.swift).
+    expect(macosAudioLifecycleChannelName, 'chanora/macos_audio_lifecycle');
+    // The wire is a no-op on the test platform (CI defaults to host OS
+    // which may be macOS or Linux). On Linux it returns early; on macOS
+    // it installs a handler. Either way, it must not throw.
+    expect(() => wireMacosAudioLifecycle(), returnsNormally);
+  });
 }