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.

docs/voice.md

@@ -178,23 +178,27 @@ Each receiver keeps an **adaptive jitter buffer per ssrc**.
 
 - Capture and playback run on miniaudio's real-time callbacks (WASAPI / CoreAudio / ALSA).
   Playback is genuinely stereo end-to-end. **Mic capture** is mono by default; **stereo mic
-  capture** is supported via `vc_set_capture_channels(stream_id, 2)` (e.g. iOS stereo built-in
-  mic via `AVAudioSession.setPreferredInputNumberOfChannels(2)`) — when enabled, the capture
-  device opens in stereo (interleaved L/R) and the encoder receives real stereo PCM (no upmix).
-  A mono mic frame on a stereo channel is upmixed L=R before encoding so the Opus bitstream is
-  still spec-correct stereo. **Screen-audio (`SCREEN_AUDIO`) loopback** captures in the
-  channel's mode — stereo when the channel is stereo (real interleaved L/R, no downmix), mono
-  when the channel is mono — so a stereo music/screen-share channel gets genuine stereo
-  end-to-end. See §9 for the platform-specific loopback mechanism.
+  capture** is supported via `vc_set_capture_channels(stream_id, 2)` — when enabled, the
+  capture device opens in stereo (interleaved L/R) and the encoder receives real stereo PCM
+  (no upmix). A mono mic frame on a stereo channel is upmixed L=R before encoding so the Opus
+  bitstream is still spec-correct stereo. **Screen-audio (`SCREEN_AUDIO`) loopback** captures
+  in the channel's mode — stereo when the channel is stereo (real interleaved L/R, no
+  downmix), mono when the channel is mono — so a stereo music/screen-share channel gets
+  genuine stereo end-to-end. See §9 for the platform-specific loopback mechanism.
 - **iOS mic capture:** all iOS audio routing is driven from Swift via `AVAudioSession` by the
   `IOSAudioRouter` singleton *before* the core (miniaudio) opens its device — miniaudio does
   NOT touch `AVAudioSession` on iOS. Input port selection (`availableInputs`), built-in mic
   orientation (`setPreferredDataSource`: front/back/top/bottom), polar patterns
   (`setPreferredPolarPattern`: omni/cardioid/subcardioid/bidirectional), mic processing mode
   (`.voiceChat` = Standard with AEC/AGC/HPF, or `.measurement` = Raw/Studio with all processing
-  off), Bluetooth mode (`.allowBluetooth` HFP voice vs `.allowBluetoothA2DP` stereo output vs
-  neither), and stereo capture (`setPreferredInputNumberOfChannels(2)` → `vc_set_capture_channels`)
-  are all set from Swift. The core then opens whatever route AVAudioSession has established.
+  off), Bluetooth mode (`.allowBluetoothHFP` HFP voice vs `.allowBluetoothA2DP` stereo output
+  vs neither), and stereo capture (`.stereo` polar pattern + `setPreferredInput` +
+  `setInputDataSource` → `vc_set_capture_channels`) are all set from Swift. The core then
+  opens whatever route AVAudioSession has established. When the user changes audio settings
+  mid-session, `IOSAudioRouter` suspends the core's devices (`vc_audio_suspend`), reconfigures
+  `AVAudioSession`, then restarts the devices (`vc_audio_restart`) so they reopen against the
+  new route — mirroring TeamTalk5's `closeSoundDevices`/`initSoundInputDevice`/
+  `initSoundOutputDevice` pattern.
 - **DSP engine: see §11.** The original plan was `webrtc-audio-processing` (AEC + NS + AGC +
   VAD in one tuned module, BSD-licensed) — but it has no working Windows/MSVC build upstream
   (confirmed via its own issue tracker: GCC-only Meson build, MinGW support unfinished, hard