Connect Apple Music and Spotify-via-Last.fm on iPhone

- Local Expo module (Swift): MusicKit authorization, Music User Token via
  MusicUserTokenProvider, and live Music app now-playing while the app is
  open (MediaPlayer notifications), reported through the device endpoint
- One-tap Apple Music onboarding on iOS; Apple Music row in Settings
- Sign in with Last.fm, plus a guided Spotify-via-Last.fm flow when direct
  Spotify sign-in is capped
- Device registration moved to shared code used by Android and iOS
Not yet compiled for iOS (no Xcode here); needs an EAS build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/mobile/app.json

@@ -9,7 +9,10 @@
     "userInterfaceStyle": "dark",
     "ios": {
       "icon": "./assets/expo.icon",
-      "bundleIdentifier": "tech.chrisedwards.musicshare"
+      "bundleIdentifier": "tech.chrisedwards.musicshare",
+      "infoPlist": {
+        "NSAppleMusicUsageDescription": "musicshare shows your friends what you play in Apple Music, and opens their songs for you."
+      }
     },
     "android": {
       "adaptiveIcon": {