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/pubspec.lock

@@ -457,10 +457,10 @@ packages:
     dependency: transitive
     description:
       name: meta
-      sha256: "23f08335362185a5ea2ad3a4e597f1375e78bce8a040df5c600c8d3552ef2394"
+      sha256: "1741988757a65eb6b36abe716829688cf01910bbf91c34354ff7ec1c3de2b349"
       url: "https://pub.dev"
     source: hosted
-    version: "1.17.0"
+    version: "1.18.0"
   mime:
     dependency: transitive
     description:
@@ -790,10 +790,10 @@ packages:
     dependency: transitive
     description:
       name: test_api
-      sha256: "8161c84903fd860b26bfdefb7963b3f0b68fee7adea0f59ef805ecca346f0c7a"
+      sha256: "949a932224383300f01be9221c39180316445ecb8e7547f70a41a35bf421fb9e"
       url: "https://pub.dev"
     source: hosted
-    version: "0.7.10"
+    version: "0.7.11"
   typed_data:
     dependency: transitive
     description: