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/ContentView.swift

@@ -16,6 +16,8 @@ struct ContentView: View {
                 .tabItem { Label("BLE", systemImage: "dot.radiowaves.left.and.right") }
             OrchestratorView()
                 .tabItem { Label("Orchestrator", systemImage: "bolt.horizontal.circle") }
+            SettingsView()
+                .tabItem { Label("Settings", systemImage: "gearshape") }
         }
         .onAppear { orchestrator.start() }
     }
@@ -25,10 +27,12 @@ struct ContentView_Previews: PreviewProvider {
     static var previews: some View {
         if #available(iOS 16.0, *) {
             let ble = BlePeripheralManager()
-            let orchestrator = ContextOrchestrator(ble: ble)
+            let spotifyAuth = SpotifyAuthManager()
+            let orchestrator = ContextOrchestrator(ble: ble, spotifyAuth: spotifyAuth)
             ContentView()
                 .environmentObject(ble)
                 .environmentObject(orchestrator)
+                .environmentObject(spotifyAuth)
         } else {
             ContentView()
         }