Phase 1: dual-track audio capture → mixed-mono 16 kHz WAV + mic VAD

AudioRecorder captures system audio (ScreenCaptureKit) + mic (AVAudioEngine) on a
single serial ioQueue, one shared monotonic t0, time-driven writers (pad gaps /
trim overlaps) so tracks stay aligned, and an energy mic-VAD for 'self' spans.
AudioMixer sums the aligned tracks into mixed_mono_16k.wav. SessionController
drives a serialized start/stop state machine, writes the session folder +
self_vad.json, exposes live level meters, and finalizes on quit.

Hardening from review: ioQueue single-domain (no races), stop() never hangs
(mic-first teardown + bounded stopCapture), layout-agnostic mic deep-copy,
discard-only video output to keep SCStream alive, VAD lockstep on committed
frames, stable signing team in project.yml, single-instance enforcement.

README.md

@@ -23,13 +23,17 @@ This repo is at **Phase 0** (scaffold, permissions, backend health check).
    ```sh
    open Ten31Transcripts.xcodeproj
    ```
-5. In Xcode, select the **Ten31Transcripts** target → **Signing & Capabilities**:
-   - Check **Automatically manage signing**.
-   - For **Team**, pick your personal team (sign in with your Apple ID — free; no
-     paid developer account needed). A stable team keeps macOS from re-asking for
-     permissions on every rebuild.
+5. Signing is preconfigured: `project.yml` sets `DEVELOPMENT_TEAM` to the free
+   personal team `BK4Y6CXN35` with automatic signing, so **Signing & Capabilities
+   should already show the team** — no manual selection needed. (If you ever sign
+   with a different Apple ID, update `DEVELOPMENT_TEAM` in `project.yml`, not in
+   Xcode — `xcodegen generate` overwrites Xcode-side changes.)
 6. Press **Run** (⌘R).
 
+> **Note:** after adding files in a new phase, re-run `xcodegen generate` and let
+> Xcode reload the project. The signing team persists because it lives in
+> `project.yml`, so macOS permissions stay granted across rebuilds.
+
 ## What Phase 0 does
 
 - Launches as a menu-bar-only app (no Dock icon).