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/src/rust/api.dart

@@ -261,6 +261,12 @@ Stream<BridgeEvent> eventsStream() =>
 Future<BridgeAudioStats> audioStats() =>
     RustLib.instance.api.crateApiAudioStats();
 
+/// Subscribe to real-time microphone input level at ~30 Hz.
+/// Values are dBFS (-120 = silence, 0 = clipping). The stream ends
+/// when the Dart subscriber cancels or the session is dropped.
+Stream<double> inputLevelStream() =>
+    RustLib.instance.api.crateApiInputLevelStream();
+
 /// Apply the P1 audio-processing config.
 Future<void> setAudioProcessingConfig({
   required BridgeAudioProcessingConfig config,
@@ -681,15 +687,22 @@ class BridgeAudioStats {
   /// Current push-to-talk state.
   final bool pttActive;
 
+  /// Current microphone input level in dBFS (-120.0 = silence, 0.0 = clipping).
+  final double inputLevel;
+
   const BridgeAudioStats({
     required this.framesSent,
     required this.framesReceived,
     required this.pttActive,
+    required this.inputLevel,
   });
 
   @override
   int get hashCode =>
-      framesSent.hashCode ^ framesReceived.hashCode ^ pttActive.hashCode;
+      framesSent.hashCode ^
+      framesReceived.hashCode ^
+      pttActive.hashCode ^
+      inputLevel.hashCode;
 
   @override
   bool operator ==(Object other) =>
@@ -698,7 +711,8 @@ class BridgeAudioStats {
           runtimeType == other.runtimeType &&
           framesSent == other.framesSent &&
           framesReceived == other.framesReceived &&
-          pttActive == other.pttActive;
+          pttActive == other.pttActive &&
+          inputLevel == other.inputLevel;
 }
 
 /// Bookmark DTO mirroring [`chanora_core::Bookmark`].