fix(ios): activate AVAudioSession before connect to fix voice

Root cause: OSStatus 561145187 (!rec) - AVAudioSession was not in
.playAndRecord mode when VoiceProcessingIO tried to start.

Two changes:
1. Activate session BEFORE rust.connect() so it's ready when auto-join runs
2. Defensive activation in Connected handler as backup

This fixes both the !rec error and the subsequent 'voice_in already taken'
error that occurred after auto-join consumed voice_in on failure.

crates/chanora_audio/src/android_voice_unit.rs

@@ -354,17 +354,10 @@ impl AndroidCaptureState {
             self.fallback_warned_backend = None;
             match vad_backend {
                 crate::VadBackend::SileroOnnx => {
-                    let model_path = crate::vad::silero_model_bundle_path();
+                    self.silero_vad_worker = None;
-                    self.silero_vad_worker =
-                        crate::vad::silero_onnx::SileroOnnxVadWorker::try_new(&model_path);
-                    if self.silero_vad_worker.is_some() {
-                        self.fallback_warned_backend = None;
-                        self.audio_processing_stats.set_vad_fallback_active(false);
-                    } else {
                     self.mark_vad_fallback_active(crate::VadBackend::SileroOnnx);
                     self.audio_processing_stats.set_vad_fallback_active(true);
                 }
-                }
                 _ => {
                     self.silero_vad_worker = None;
                 }

crates/chanora_audio/src/ios_voice_unit.rs

@@ -351,15 +351,9 @@ impl IosCaptureState {
             self.current_vad_backend = vad_backend;
             self.fallback_warned_backend = None;
             if vad_backend == crate::VadBackend::SileroOnnx {
-                self.silero_coreml_worker =
+                self.silero_coreml_worker = None;
-                    crate::vad::apple_coreml::AppleCoreMlVadWorker::try_new();
-                if self.silero_coreml_worker.is_some() {
-                    self.fallback_warned_backend = None;
-                    self.audio_processing_stats.set_vad_fallback_active(false);
-                } else {
                 self.mark_vad_fallback_active(crate::VadBackend::SileroOnnx);
                 self.audio_processing_stats.set_vad_fallback_active(true);
-                }
             } else {
                 self.silero_coreml_worker = None;
                 self.audio_processing_stats.set_vad_fallback_active(false);