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/iOS/VoiceCatiOS/SessionState.swift

@@ -204,6 +204,11 @@ final class SessionState {
         if result == .ok {
             voiceState.micActive = true
             voiceState.localStreamId = streamId
+            // Publish the active mic stream ID so IOSAudioRouter can reset the core's capture
+            // channel count when the user switches mono↔stereo (selectCaptureChannels /
+            // applyPreset). Without this, switching stereo→mono leaves the LocalStream's
+            // capture_channels field at 2 and the next engine start still opens stereo.
+            AudioSessionManager.shared.activeMicStreamId = streamId
             // Apply the user's capture channel selection (mono/stereo) from IOSAudioRouter.
             // The core opens the capture device via miniaudio on the next engine start;
             // vc_set_capture_channels tells it to open in stereo (2) or mono (1).
@@ -220,6 +225,7 @@ final class SessionState {
         if voiceState.localStreamId != 0 {
             client.stopStream(voiceState.localStreamId)
             voiceState.localStreamId = 0
+            AudioSessionManager.shared.activeMicStreamId = nil
         }
         voiceState.micActive = false
         voiceState.level = 0