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/Info.plist

@@ -2,6 +2,17 @@
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>
+	<key>CFBundleURLTypes</key>
+	<array>
+		<dict>
+			<key>CFBundleURLName</key>
+			<string>sh.nym.iris.spotify-auth</string>
+			<key>CFBundleURLSchemes</key>
+			<array>
+				<string>iris-spotify-auth</string>
+			</array>
+		</dict>
+	</array>
 	<key>MKDirectionsApplicationSupportedModes</key>
 	<array/>
 	<key>NSCalendarsFullAccessUsageDescription</key>