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.

Ten31Transcripts/App/Ten31TranscriptsApp.swift

@@ -10,9 +10,16 @@ import SwiftUI
 struct Ten31TranscriptsApp: App {
     @NSApplicationDelegateAdaptor(AppDelegate.self) private var appDelegate
 
-    @StateObject private var settings = AppSettings()
+    @StateObject private var settings: AppSettings
     @StateObject private var permissions = PermissionsManager()
     @StateObject private var health = SparkControlHealth()
+    @StateObject private var session: SessionController
+
+    init() {
+        let settings = AppSettings()
+        _settings = StateObject(wrappedValue: settings)
+        _session = StateObject(wrappedValue: SessionController(settings: settings))
+    }
 
     var body: some Scene {
         MenuBarExtra {
@@ -20,8 +27,9 @@ struct Ten31TranscriptsApp: App {
                 .environmentObject(settings)
                 .environmentObject(permissions)
                 .environmentObject(health)
+                .environmentObject(session)
         } label: {
-            Image(systemName: "waveform.circle")
+            Image(systemName: session.state == .recording ? "waveform.circle.fill" : "waveform.circle")
         }
         .menuBarExtraStyle(.window)
     }