Fix Android support, add settings persistence, and clean up code

[Mihonarium]

Summary

Android Foreground Service (new)

• Reliable background audio on Android: Created android-foreground-service Expo native module with a Kotlin ForegroundService using mediaPlayback type
• Shows a minimal, silent persistent notification ("Sonic Compass is running" / current heading when backgrounded)
• Config plugin auto-injects service declaration and FOREGROUND_SERVICE_MEDIA_PLAYBACK + POST_NOTIFICATIONS permissions into AndroidManifest.xml
• JS bridge with platform guard (no-op on iOS)
• Foreground service starts when audio initializes, stops on app cleanup
• Notification updates with current heading every 2s when backgrounded

Previous fixes (still in this PR)

• Fix Android support: Guard native BackgroundHaptics import with Platform.OS check, add proper Android vibration fallback
• Fix audio mode: Change from DoNotMix to DuckOthers so the app doesn't kill other apps' audio
• Add settings persistence: Save/load settings via AsyncStorage
• Code quality cleanup: Remove duplicates in app.json, dead code, unused imports, fix stale closures
• Restore setLastDir: Keeps track of last directional sound timestamp

Architecture

android-foreground-service/
├── expo-module.config.json     # platforms: ["android"]
├── package.json
├── src/
│   ├── index.js                # JS API: startService/stopService/updateNotification
│   └── module.js               # Platform guard (no-op on iOS)
├── android/
│   ├── build.gradle
│   └── src/main/java/.../
│       ├── AndroidForegroundServiceModule.kt   # Expo module bridge
│       └── CompassForegroundService.kt         # Android Service class
└── plugin/
    └── withForegroundService.js  # Config plugin for AndroidManifest

Test plan

• Build and test on iOS - verify all existing functionality works unchanged
• Build and test on Android - verify app launches, compass works, sounds play, vibration works
• Critical: Test background mode on Android for 10+ minutes - audio and vibration should continue indefinitely
• Verify persistent notification appears on Android when app is backgrounded
• Verify notification shows current heading when backgrounded
• Verify settings persist across app restarts on both platforms
• Verify audio mixes properly with other apps (music, calls)

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