Feature request: iOS lock screen controls and Android MediaSession for background playback

## Current state (v1.6.0)

`playInBackground` + `notificationTitle`/`notificationText` provide a MediaStyle
notification on Android. However:

- **iOS has no lock screen / control center presence at all** — no Now Playing
info, no remote commands, and playback does not resume after interruptions
(phone calls, alarms)
- **Android notification has no `MediaSessionCompat`** — so it does not appear
in the media carousel / lock screen on Android 11+, and Bluetooth/headset
media buttons are not handled
- No artwork (thumbnail) on either platform

## Proposal

- **iOS**: `MPNowPlayingInfoCenter` + `MPRemoteCommandCenter` (play/pause),
and auto-resume after interruptions via the `shouldResume` hint
- **Android**: back the existing notification with a `MediaSessionCompat`
(media carousel, lock screen, media buttons)
- Both: optional artwork, e.g. `notification={{ title, description, thumbnail }}`

Start by locating the existing Android MediaStyle notification and the iOS playback interruption handling, then review the proposed MPNowPlayingInfoCenter, MPRemoteCommandCenter, and MediaSessionCompat integrations. Done means both platforms expose lock-screen controls, playback resumes when appropriate, and optional artwork is supported.

Written by the indexing model from the issue text.