feat(voice): real-time mic input level metering at 30 Hz (#25)

* feat(voice): add real-time mic input level metering at 30 Hz

Expose input RMS from the audio engine through the bridge as a
dedicated Rust→Dart Stream<double>, replacing the binary on/off
indicator with a proportional dBFS level meter.

Rust side:
- chanora_audio: add set_input_dbfs/input_dbfs accessors to
  SharedAudioProcessingStats; restructure CaptureState::ingest()
  to compute dBFS from mono buffer before the PTT guard so the
  meter shows mic activity even when not transmitting.
- chanora_core: widen audio_stats() return to include f32 input
  level.
- chanora_bridge: add input_level: f32 to BridgeAudioStats and
  new input_level_stream(sink: StreamSink<f32>) that pushes at
  ~30 Hz via tokio interval task.
- Update frb_generated.rs serialization for the new field.

Flutter side:
- VoiceLevelMeter: accept optional double level (dBFS), map
  -60..0 dBFS to 0..1 fill fraction, animate with
  TweenAnimationBuilder for smooth transitions.
- voice_compact.dart: subscribe to inputLevelStream in the voice
  details sheet for 30 Hz meter updates, keeping 250 ms poll for
  TX/RX counters.
- voice_bar.dart: accept optional inputLevel from the stream.
- main.dart: subscribe to inputLevelStream, pass to VoiceBar.

* chore: sync Flutter build config and dependency updates

- Add Flutter migrator flags to gradle.properties (builtInKotlin, newDsl)
- Add FlutterGeneratedPluginSwiftPackage to iOS/macOS Xcode projects
- Update meta 1.17→1.18, test_api 0.7.10→0.7.11
- Rebuild chanora_bridge framework for macOS
- Update Podfile.lock for iOS and macOS

* fix(voice): correct meter animation, pre-gain dBFS, stream lifecycle, and protocol warnings

B1: Convert VoiceLevelMeter to StatefulWidget tracking previous fill
     as Tween begin so the meter animates smoothly instead of resetting
     to zero on every frame.

B2: Compute dBFS from pre-gain mono samples in CaptureState::ingest()
     so the level meter reflects raw mic input, matching mobile paths.

B4: End input_level_stream after 10 consecutive session errors instead
     of emitting -120 dBFS forever when the session is gone.

Also fixes all 13 clippy warnings in chanora_protocol: collapsed
nested if-let patterns, replaced .ok() + Some matching with Ok, used
? operator, and introduced EventChannels struct to reduce the four
helper functions below the 7-argument threshold.

* fix(voice): use MissedTickBehavior::Skip for level meter stream and align dBFS doc

Set MissedTickBehavior::Skip on the input_level_stream tokio interval
so slow audio_stats() calls skip missed ticks instead of bursting,
preventing CPU spikes on the UI meter thread.

Align VoiceLevelMeter class doc: the mapping floors at -60 dBFS
(via dbfsToFraction), not the full -120 range.

apps/chanora_flutter/lib/main.dart

@@ -312,6 +312,7 @@ class _BetaHomeState extends State<_BetaHome> with WidgetsBindingObserver {
   rust.BridgeSnapshot? _snapshot;
   final List<String> _uiDiagnostics = [];
   rust.BridgeAudioStats? _audioStats;
+  double? _inputLevel;
   Timer? _statsTimer;
   bool _snapshotRefreshInFlight = false;
   bool _snapshotRefreshQueued = false;
@@ -319,6 +320,7 @@ class _BetaHomeState extends State<_BetaHome> with WidgetsBindingObserver {
   bool _snapshotRefreshQueuedReportErrors = false;
   int _connectionEpoch = 0;
   StreamSubscription<rust.BridgeEvent>? _eventsSub;
+  StreamSubscription<double>? _inputLevelSub;
   late final PrefetchDebouncer _prefetch;
 
   // v1 voice subsystem state (SDD-094/095/096/097). Driven by
@@ -395,6 +397,9 @@ class _BetaHomeState extends State<_BetaHome> with WidgetsBindingObserver {
     _prefetch = PrefetchDebouncer(onPrefetch: _onPrefetchServer);
     _hostCtl.addListener(_onHostEdited);
     _eventsSub = rust.eventsStream().listen(_onEvent);
+    _inputLevelSub = rust.inputLevelStream().listen((level) {
+      if (mounted) setState(() => _inputLevel = level);
+    });
     // SDD-106 §5: subscribe to Kotlin -> Dart permissionStateChanged
     // events as early as possible so the listen-only banner reflects
     // the system state on first frame.
@@ -957,6 +962,7 @@ class _BetaHomeState extends State<_BetaHome> with WidgetsBindingObserver {
     WidgetsBinding.instance.removeObserver(this);
     HardwareKeyboard.instance.removeHandler(_handleFocusedPttKey);
     _eventsSub?.cancel();
+    _inputLevelSub?.cancel();
     _statsTimer?.cancel();
     _snapshotRefreshInFlight = false;
     _snapshotRefreshQueued = false;
@@ -2378,6 +2384,7 @@ class _BetaHomeState extends State<_BetaHome> with WidgetsBindingObserver {
                         _currentVoiceChannelId,
                       ),
                       audioStats: _audioStats,
+                      inputLevel: _inputLevel,
                       pttLevel: _pttLevel,
                       pttBackendId: _pttBackendId,
                       pttBoundInputClass: _pttBoundInputClass,