docs(flutter): add dart doc comments to core services and widgets (TODO-085)

Add dart doc comments to poke_notification_service, poke_preferences_service,
link_trust_service, voice_settings, snapshot_view covering public API.

apps/chanora_flutter/lib/widgets/voice_settings.dart

@@ -19,7 +19,8 @@ import 'voice_platform.dart';
 import 'voice_settings_controls.dart';
 import '../src/rust/api.dart' as rust;
 
-/// Result returned by [VoiceSettingsDialog].
+/// Result returned by [VoiceSettingsDialog] when the user saves or
+/// requests a key bind.
 class VoiceSettingsResult {
   const VoiceSettingsResult({
     required this.mode,
@@ -34,7 +35,15 @@ class VoiceSettingsResult {
   final rust.BridgeAudioProcessingConfig audioConfig;
 }
 
-/// Voice + audio processing settings dialog.
+/// Dialog for configuring voice transmission and audio processing settings.
+///
+/// Surfaces transmit mode selection (continuous, PTT, voice-activity),
+/// PTT release-tail slider, key-bind request, and a full audio processing
+/// panel covering noise suppression, echo cancellation, AGC, HPF, and VAD
+/// backend selection.
+///
+/// On mobile hosts, the voice-activity segment is hidden when no
+/// Chanora-owned VAD pipeline is available (iOS, macOS, web).
 class VoiceSettingsDialog extends StatefulWidget {
   const VoiceSettingsDialog({
     super.key,