feat(ios): audio overhaul, Join/Leave Voice, channel-id sync fix, stereo mic capture

Three iOS client problems fixed plus a new core stereo-mic capture ABI:

1. Channel-id sync bug (mic button permanently dimmed): SessionState never
   synced currentChannelId from the self user's channelId on connect, so the
   mic button (gated on currentChannelId == 0) stayed dimmed. Added
   syncSelfChannel() (mirrors macOS MainWindowController.swift:461,491,522);
   called from init/.channelList/.userJoined/.userLeft/.userUpdated/.joinResult.
   Added applyServerMuteState() + serverMuted/serverDeafened to VoiceState.

2. Join/Leave Voice button: replaced icon-only mic toggle with explicit
   text button (parity with macOS). Mute/deafen disable when not in voice.

3. IOSAudioRouter.swift (new): full AVAudioSession routing layer — input
   port selection, built-in mic orientation/polar patterns, Bluetooth
   HFP/A2DP/Off modes, Standard/Raw mic processing, stereo capture, AirPlay,
   UserDefaults persistence. AudioSessionManager delegates to it.

4. Core stereo-mic capture (append-only ABI): vc_set_capture_channels()
   lets the core open the mic device in stereo (2-ch interleaved). LocalStream
   gains capture_channels; ensure_audio_running reads it; audio_engine.cpp
   capture_accum_ + on_capture updated to channel-aware accumulation. Test
   test_stereo_mic_capture (headless, L!=R stereo round-trip). Swift wrapper
   VoiceCatClient.setCaptureChannels.

5. Settings UI rework: AVAudioSession-derived input/output tree replaces
   miniaudio device picker.

6. iOS deployment target raised to 18.0 (Package.swift + project.pbxproj).
   swift-tools-version 6.0 with swiftLanguageModes .v5.

Docs: tech-stack.md, architecture.md, voice.md, roadmap.md, building.md
updated; stale 'vc_audio_suspend/resume deferred' claims corrected.

Verified: ctest --preset dev 21/21 green; swift test 6/6 green;
xcodebuild -target VoiceCatiOS -sdk iphonesimulator BUILD SUCCEEDED.

PROGRESS.md

@@ -172,8 +172,56 @@ up instantly. Newest status at the top.
     controls the *mic* path which still uses miniaudio's device.
 
 
-- **Planned (not started):** **iOS audio overhaul + Join/Leave Voice + channel-id sync fix**
-  (2026-06-19, plan written on Windows; implement on Mac). Three problems found while reviewing
+- **Done:** **iOS audio overhaul + Join/Leave Voice + channel-id sync fix** (2026-06-19).
+  Three problems found while reviewing the iOS client, all fixed:
+  1. **Mic button permanently dimmed (BUG — fixed).** `VoiceControlsView.swift:26` gated the
+     mic button on `session.currentChannelId == 0`, but `SessionState` never synced
+     `currentChannelId` from the self user's `channelId` on connect. The server auto-places
+     every newly-authed user into the Lobby (channel 1, `server/src/session_registry.cpp:111`),
+     but the iOS client ignored it. **Fix:** added `syncSelfChannel()` (mirrors macOS
+     `MainWindowController.swift:461,491,522`); called from `init`, `.channelList`,
+     `.userJoined`/`.userLeft`/`.userUpdated`, `.joinResult`. Added
+     `applyServerMuteState(muted:deafened:)` (mirrors macOS lines 693-700); called from
+     `.userUpdated`. Added `serverMuted`/`serverDeafened` to `VoiceState`.
+  2. **No Join/Leave Voice button (fixed — parity with macOS).** Replaced the icon-only mic
+     toggle with an explicit "Join Voice"/"Leave Voice" text button (mirrors macOS
+     `micToggleButton`). Mute/deafen buttons now disable when not in voice. PTT path kept.
+  3. **Limited audio input/output options (fixed — full `IOSAudioRouter.swift`).** New
+     `IOSAudioRouter` singleton drives all iOS audio routing via `AVAudioSession` before the
+     core (miniaudio) opens its device: input port selection (`availableInputs`), built-in mic
+     orientation (`setPreferredDataSource`: front/back/top/bottom), polar patterns
+     (`setPreferredPolarPattern`: omni/cardioid/subcardioid/bidirectional), Bluetooth mode
+     (`.allowBluetooth` HFP voice / `.allowBluetoothA2DP` stereo output / neither), mic
+     processing mode (`.voiceChat` Standard with AEC/AGC/HPF / `.measurement` Raw with all
+     processing off + speaker echo warning), stereo capture
+     (`setPreferredInputNumberOfChannels(2)` → `vc_set_capture_channels`), AirPlay via
+     `AVRoutePickerView`. All choices persisted in `UserDefaults`; re-applied on route changes.
+     `AudioSessionManager` refactored to delegate routing to `IOSAudioRouter`.
+  4. **Core stereo-mic capture (new C ABI: `vc_set_capture_channels`).** Append-only ABI
+     addition: `vc_result vc_set_capture_channels(vc_client*, uint32_t stream_id, uint32_t
+     channels)` (1=mono, 2=stereo). `LocalStream` gained a `capture_channels` field;
+     `ensure_audio_running()` reads it into `AudioParams.capture_channels` before the device
+     opens. `audio_engine.cpp` `capture_accum_` sized to `frame_samples_ * capture_channels`;
+     `on_capture` updated to the same channel-aware accumulation pattern as `on_loopback`.
+     Skeleton stub added. Test `test_stereo_mic_capture` (headless, feeds L≠R stereo through
+     the mic accumulator path, asserts L≠R end-to-end). `ctest --preset dev` — **21/21 green**.
+     Swift wrapper: `VoiceCatClient.setCaptureChannels(streamId:channels:)`.
+  5. **Settings UI rework.** `SettingsView` replaced the miniaudio-based device picker with
+     the AVAudioSession-derived tree: Audio Input (port picker → built-in mic
+     orientation/polar pattern sub-pickers + mic mode Standard/Raw + channels Mono/Stereo),
+     Audio Output (bluetooth mode + current route read-only + AirPlay), Voice (input mode,
+     VAD threshold).
+  6. **Deployment target raised to iOS 18.0.** `Package.swift` + `project.pbxproj` (4
+     occurrences). Unlocks newest AVAudioSession APIs.
+  7. **Docs updated:** `docs/tech-stack.md` §2 (iOS audio routing via IOSAudioRouter, stereo
+     mic, deployment 18.0, fixed stale "deferred" claim about `vc_audio_suspend`/`resume`),
+     `docs/architecture.md` §4 (Swift binding notes — IOSAudioRouter, fixed stale "deferred"
+     claim), `docs/voice.md` (new iOS mic capture subsection), `docs/roadmap.md` (iOS pending
+     list updated), `docs/building.md` §9 (deployment target 18.0), `PROGRESS.md` (this entry).
+  - **Verified:** `cmake --build --preset dev` + `ctest --preset dev` — **21/21 green**
+    (including new `test_stereo_mic_capture`: `total_diff=8433549, seen_channels=2`).
+  - **Original plan (kept for reference):**
+  Three problems found while reviewing
   the iOS client:
   1. **Mic button permanently dimmed (BUG — root cause).** `VoiceControlsView.swift:26` gates the
      mic button on `session.currentChannelId == 0`, but `SessionState` never syncs