Add Spotify integration with toggleable music source

- Add OAuth 2.0 PKCE authentication for Spotify Web API
- Create SpotifyNowPlayingMonitor for polling current track
- Add Settings tab with music source toggle (Apple Music/Spotify)
- Store tokens securely in Keychain
- Display current track on Glass as NOW_PLAYING card

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

IrisCompanion/iris/irisApp.swift

@@ -12,12 +12,15 @@ struct irisApp: App {
     @Environment(\.scenePhase) private var scenePhase
     @StateObject private var ble: BlePeripheralManager
     @StateObject private var orchestrator: ContextOrchestrator
+    @StateObject private var spotifyAuth: SpotifyAuthManager
 
     init() {
         let bleManager = BlePeripheralManager()
         bleManager.start()
+        let spotify = SpotifyAuthManager()
         _ble = StateObject(wrappedValue: bleManager)
-        _orchestrator = StateObject(wrappedValue: ContextOrchestrator(ble: bleManager))
+        _spotifyAuth = StateObject(wrappedValue: spotify)
+        _orchestrator = StateObject(wrappedValue: ContextOrchestrator(ble: bleManager, spotifyAuth: spotify))
     }
 
     var body: some Scene {
@@ -25,6 +28,12 @@ struct irisApp: App {
             ContentView()
                 .environmentObject(ble)
                 .environmentObject(orchestrator)
+                .environmentObject(spotifyAuth)
+                .onOpenURL { url in
+                    if url.scheme == "iris-spotify-auth" {
+                        spotifyAuth.handleCallback(url: url)
+                    }
+                }
                 .onChange(of: scenePhase) { phase in
                     if phase == .active || phase == .background {
                         ble.start()