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/AppState.swift

@@ -159,6 +159,17 @@ final class AppState {
                 connectStatus = ""
                 showPasswordPrompt = false
                 self.session = newSession
+                // Activate the audio session now, while connected — NOT lazily when the first
+                // remote stream arrives. The core opens its miniaudio playback device the moment
+                // a remote stream starts and only THEN emits .streamStarted; if we waited for
+                // that event to activate, the playback device would open against an inactive
+                // AVAudioSession and produce no sound (the "can't hear anyone" bug). Activating
+                // here guarantees the session is live before any device opens.
+                do {
+                    try AudioSessionManager.shared.ensureSessionActive()
+                } catch {
+                    print("Audio session activate on connect failed: \(error)")
+                }
             } else {
                 connectStatus = "Auth failed: \(ev.result.description)"
                 showPasswordPrompt = true