fix(ios): stereo mic + A2DP output, add vc_audio_restart ABI

Diagnosed by comparing against TeamTalk5 (Client/iTeamTalk), which
achieves stereo mic + A2DP output. Five fixes:

1. configureStereoCapture now calls setPreferredInput +
   setInputDataSource (mirroring TeamTalk5's SoundDevicesModel).
   Previously omitted based on incorrect diagnosis that
   setPreferredInput collapsed A2DP — the real culprit was
   setPreferredInputNumberOfChannels(2), which neither project uses.

2. New C ABI: vc_audio_restart (full stop + re-init, unlike
   suspend/resume which only stop/start). Swift wrapper added.
   The withAudioSuspend wrapper that used it was removed after
   on-device testing showed it killed all audio (including
   VoiceOver) when switching presets — the core's
   set_capture_channels handles engine restart internally.

3. Bluetooth options: Voice Chat preset now includes BOTH
   .allowBluetoothHFP AND .allowBluetoothA2DP (matching TeamTalk5's
   UtilSound.swift:228). Previously HFP-only blocked A2DP headphones.

4. Capture channels now reset when switching stereo→mono via
   selectCaptureChannels/applyPreset. AudioSessionManager tracks
   activeMicStreamId (set by SessionState on join/leave voice).

5. Docs synced: voice.md, tech-stack.md, architecture.md,
   PROGRESS.md. Removed stale setPreferredInputNumberOfChannels(2)
   references.

Verified: ctest --preset dev 21/21 green, iOS client builds.
Stereo mic + A2DP output still needs on-device debugging — the
core recipe is correct but iOS 26 route behavior requires
hands-on testing with a debugger.

clients/apple/Sources/VoiceCatCore/VoiceCatClient.swift

@@ -344,6 +344,19 @@ public final class VoiceCatClient {
         VoiceCatResult(vc_audio_resume(handle))
     }
 
+    /// Full audio engine restart — uninitialize and re-initialize the capture and playback
+    /// devices so they pick up a new AVAudioSession route. Call this AFTER reconfiguring
+    /// AVAudioSession (setCategory, setPreferredInput, setPreferredPolarPattern, etc.) so the
+    /// core's devices reopen against the new route. Unlike `audioSuspend()`/`audioResume()`
+    /// (which only stop/start the existing devices, leaving them bound to the route that was
+    /// active when they were opened), this fully re-initializes them. Mirrors TeamTalk5's
+    /// closeSoundDevices()/initSoundInputDevice()/initSoundOutputDevice() pattern. Safe to
+    /// call when the engine is not running (it will just start it).
+    @discardableResult
+    public func audioRestart() -> VoiceCatResult {
+        VoiceCatResult(vc_audio_restart(handle))
+    }
+
     // MARK: - Receive-side, per remote stream (LOCAL — no protocol traffic; docs/voice.md §10)
 
     @discardableResult