fix: improve voice and chat controls

apps/chanora_flutter/lib/widgets/voice_settings.dart

@@ -67,6 +67,7 @@ class VoiceSettingsDialog extends StatefulWidget {
     this.pttLevel = '',
     this.pttBackendId = '',
     this.pttBoundInputClass = '',
+    this.onnxRuntimeAvailable = true,
     this.talkPower,
     this.neededTalkPower,
     this.talkPowerGranted,
@@ -78,6 +79,7 @@ class VoiceSettingsDialog extends StatefulWidget {
   final String pttLevel;
   final String pttBackendId;
   final String pttBoundInputClass;
+  final bool onnxRuntimeAvailable;
   final int? talkPower;
   final int? neededTalkPower;
   final bool? talkPowerGranted;
@@ -101,6 +103,10 @@ class _VoiceSettingsDialogState extends State<VoiceSettingsDialog> {
     _audioProcessing = AudioProcessingConfigState.fromConfig(
       widget.initialAudioConfig,
     );
+    _audioProcessing.vadBackend = normalizedVadBackend(
+      _audioProcessing.vadBackend,
+      onnxRuntimeAvailable: widget.onnxRuntimeAvailable,
+    );
   }
 
   rust.BridgeAudioProcessingConfig _buildConfig() {
@@ -291,17 +297,24 @@ class _VoiceSettingsDialogState extends State<VoiceSettingsDialog> {
               const VoiceSubHeader('Backend'),
               SegmentedButton<rust.BridgeVadBackend>(
                 style: voiceSegmentedButtonStyle(theme),
-                segments: _isDesktopSileroVadHost
-                    ? desktopVadBackendSegments
-                    : vadBackendSegments,
+                segments: vadBackendSegmentsForAvailability(
+                  desktop: _isDesktopSileroVadHost,
+                  onnxRuntimeAvailable: widget.onnxRuntimeAvailable,
+                ),
                 selected: {_audioProcessing.vadBackend},
-                onSelectionChanged: (s) =>
-                    setState(() => _audioProcessing.vadBackend = s.first),
+                onSelectionChanged: (s) => setState(
+                  () => _audioProcessing.vadBackend = normalizedVadBackend(
+                    s.first,
+                    onnxRuntimeAvailable: widget.onnxRuntimeAvailable,
+                  ),
+                ),
               ),
               const SizedBox(height: 8),
               if (_isDesktopSileroVadHost)
                 Text(
-                  'Silero gives the best quality when ONNX Runtime is installed. WebRTC works without ONNX Runtime and is the safer fallback if Linux setup is incomplete.',
+                  widget.onnxRuntimeAvailable
+                      ? 'Silero gives the best quality when ONNX Runtime is installed. WebRTC works without ONNX Runtime and is the safer fallback if Linux setup is incomplete.'
+                      : 'Silero is unavailable because ONNX Runtime was not found. WebRTC is selected until libonnxruntime.so is installed or bundled.',
                   style: theme.textTheme.bodySmall?.copyWith(
                     color: theme.colorScheme.onSurfaceVariant,
                   ),