feat(audio,bridge,flutter): v1 audio + PTT lifecycle implementation (SDD-094..097)

Implement the SDD-094 / SDD-095 / SDD-096 / SDD-097 detailed designs
committed in dfa84ee.

Rust side
- chanora_audio::TransmitMode enum (Ptt/Continuous/VoiceActivity) with
  serde-friendly u8 repr (SDD-095).
- chanora_audio::TransmitModeSelector: lock-free Atomic-backed selector
  that is the sole writer of transmit_active (per SAD-083), applying
  hard_mute as a final clamp. VoiceActivity falls through to Continuous
  for v1 (DEC-030 placeholder).
- chanora_audio::ReleaseTailTimer: tokio-task-owning struct driving the
  selector's ptt_held input; default 200 ms tail, configurable 0–500 ms
  with AtomicU32 hot read; pending JoinHandle held in a std::sync::Mutex
  touched only on PTT edge transitions (SDD-096).
- chanora_storage: AudioMeta persisted as audio_meta.json next to
  identity.dek; get/set_transmit_mode + get/set_release_tail_ms with
  0..=500 clamp on write.
- chanora_core::ChanoraSession: voice_join(channel, password) and
  voice_leave() are the new lifecycle entry points; ensure_audio_running
  and shutdown_audio_if_idle are private helpers around the existing
  Option<AudioEngine> field. SessionEvent::VoiceState carries the
  in_channel / transmit_mode / mute / release_tail_ms tuple. Selector
  state survives reconnect; supervisor rewires it to each fresh engine
  gate.
- chanora_bridge: drop start_audio; add voice_join, voice_leave,
  set/get_transmit_mode, set/get_release_tail_ms, set_hard_mute.
  BridgeEvent::VoiceState mirrors the core event. AudioStarted/Stopped
  kept for backwards compat but Flutter ignores them in the new UI.

Flutter side
- New apps/chanora_flutter/lib/widgets/voice_bar.dart replaces the
  legacy _AudioControls widget. Renders channel pill, mode badge,
  mute toggle, level meter, PttCapabilityBadge, leave button. No
  manual Start affordance anywhere.
- New apps/chanora_flutter/lib/widgets/voice_settings.dart dialog with
  TransmitMode radio group (VoiceActivity disabled with 'Coming soon'
  trailing label per DEC-030), bind-key button, release-tail slider
  0–500 ms step 25.
- main.dart: state fields _inChannel, _transmitMode, _hardMute,
  _releaseTailMs driven by BridgeEvent_VoiceState. Channel-tap now
  calls voiceJoin instead of moveToChannel. Removed _onStartAudio,
  _audioStarted-gated branch, and the FilledButton.
- l10n: 11 new strings in app_en.arb + app_zh.arb.

Verification
- cargo check --workspace: clean.
- cargo test --workspace --lib: 72 passed / 0 failed / 1 ignored
  (chanora_audio: +12 new tests for TransmitMode/Selector/ReleaseTail;
  chanora_storage: +2 new tests for audio_meta round-trip).
- flutter analyze: 0 errors, 0 warnings; 6 infos are the Flutter 3.32
  Radio.groupValue deprecation (pre-existing API usage).
- FRB Dart/Rust bindings regenerated via flutter_rust_bridge_codegen.

Follow-up (intentionally deferred)
- PttController and per-platform PTT backends still drive AudioTransmitGate
  directly via the legacy set_ptt path; routing those key edges through
  ChanoraSession::release_tail_timer().{key_down,key_up} so the tail
  applies to native PTT input is a contained wiring change in a follow-up.
- Real audio-level RMS in BridgeAudioStats (current meter is binary).
- VoiceActivity backend (DEC-030).

apps/chanora_flutter/lib/src/rust/api.dart

@@ -9,8 +9,8 @@ import 'package:flutter_rust_bridge/flutter_rust_bridge_for_generated.dart';
 import 'package:freezed_annotation/freezed_annotation.dart' hide protected;
 part 'api.freezed.dart';
 
-// These functions are ignored because they are not marked as `pub`: `log_sink`, `runtime`, `session`
-// These function are ignored because they are on traits that is not defined in current crate (put an empty `#[frb]` on it to unignore): `clone`, `clone`, `clone`, `clone`, `clone`, `clone`, `clone`, `clone`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `from`, `from`, `from`, `from`, `from`, `from`
+// These functions are ignored because they are not marked as `pub`: `log_sink`, `runtime`, `session`, `transmit_mode_from_u8`
+// These function are ignored because they are on traits that is not defined in current crate (put an empty `#[frb]` on it to unignore): `clone`, `clone`, `clone`, `clone`, `clone`, `clone`, `clone`, `clone`, `clone`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `fmt`, `from`, `from`, `from`, `from`, `from`, `from`, `from`, `from`
 
 /// Connect to a TeamSpeak-compatible server and return the initial
 /// state snapshot. Honours the DEC-006 single-connection invariant
@@ -37,14 +37,50 @@ Future<void> disconnect() => RustLib.instance.api.crateApiDisconnect();
 /// True if a connection is currently active.
 Future<bool> isConnected() => RustLib.instance.api.crateApiIsConnected();
 
-/// Start the audio engine on the active connection. Requires a
-/// connection; idempotent (will replace any previous engine).
-Future<void> startAudio() => RustLib.instance.api.crateApiStartAudio();
-
 /// Set the push-to-talk state.
+///
+/// Superseded in v1 by [`set_transmit_mode`] + the binding capture
+/// dialog. Retained so legacy callers and integration tests keep
+/// working; the new VoiceBar UI no longer invokes this.
 Future<void> setPtt({required bool active}) =>
     RustLib.instance.api.crateApiSetPtt(active: active);
 
+/// Join a voice channel (SDD-094). Moves the user to `channel_id`,
+/// brings up the audio engine if needed, and emits
+/// `BridgeEvent::VoiceState`. `password` may be empty.
+Future<void> voiceJoin({required BigInt channelId, required String password}) =>
+    RustLib.instance.api.crateApiVoiceJoin(
+      channelId: channelId,
+      password: password,
+    );
+
+/// Leave the current voice channel (SDD-094). Tears down the audio
+/// engine and emits `BridgeEvent::VoiceState`.
+Future<void> voiceLeave() => RustLib.instance.api.crateApiVoiceLeave();
+
+/// Set the active transmit mode (SDD-095).
+Future<void> setTransmitMode({required BridgeTransmitMode mode}) =>
+    RustLib.instance.api.crateApiSetTransmitMode(mode: mode);
+
+/// Read the active transmit mode.
+Future<BridgeTransmitMode> getTransmitMode() =>
+    RustLib.instance.api.crateApiGetTransmitMode();
+
+/// Update the release-tail in milliseconds (SDD-096). Values are
+/// clamped to `0..=500` on the Rust side; passing anything larger
+/// silently saturates.
+Future<void> setReleaseTailMs({required int ms}) =>
+    RustLib.instance.api.crateApiSetReleaseTailMs(ms: ms);
+
+/// Read the current release-tail in milliseconds.
+Future<int> getReleaseTailMs() =>
+    RustLib.instance.api.crateApiGetReleaseTailMs();
+
+/// Engage or release the hard-mute clamp (SDD-094). When `true`
+/// the audio engine transmits nothing regardless of mode.
+Future<void> setHardMute({required bool muted}) =>
+    RustLib.instance.api.crateApiSetHardMute(muted: muted);
+
 /// Update the active PTT binding (gen2 v0.9.3 / DEC-026). The
 /// platform_key string is opaque to the bridge — it identifies the
 /// bound key inside the platform backend and never appears in any
@@ -362,6 +398,23 @@ sealed class BridgeEvent with _$BridgeEvent {
     /// `"mouse-side-button"`); empty when no binding is active.
     required String boundInputClass,
   }) = BridgeEvent_PttCapability;
+
+  /// Voice subsystem state snapshot (SDD-094). The Flutter
+  /// VoiceBar listens to this stream.
+  const factory BridgeEvent.voiceState({
+    /// True when the session is currently joined to a voice
+    /// channel and the audio engine is running.
+    required bool inChannel,
+
+    /// Active transmit mode.
+    required BridgeTransmitMode transmitMode,
+
+    /// True when the hard-mute clamp is engaged.
+    required bool mute,
+
+    /// Current release-tail in milliseconds (0..=500).
+    required int releaseTailMs,
+  }) = BridgeEvent_VoiceState;
 }
 
 /// Coarse OS-reported network state. Mirrors
@@ -440,3 +493,17 @@ class BridgeSnapshot {
           channels == other.channels &&
           clients == other.clients;
 }
+
+/// Voice transmit mode mirror (SDD-095). Schema-controlled enum;
+/// the wire encoding matches [`chanora_core::TransmitMode::as_u8`].
+enum BridgeTransmitMode {
+  /// Push-to-talk (default).
+  ptt,
+
+  /// Continuous transmission while in channel and not muted.
+  continuous,
+
+  /// Voice-activity detection — reserved per DEC-030; v1 behaves
+  /// as `Continuous`.
+  voiceActivity,
+}