Lagrange 2.1.1 issue #379 test build

This prerelease tests audiobook playback while Lagrange is backgrounded and the user switches to another app. It includes the merged fix for the MediaLibraryService notification and foreground-playback regression.

Fixes

• Restored audiobook Media3 notification publication after the Android Auto/MediaLibraryService migration.
• Promoted active audiobook playback to a media foreground service with a session-linked notification that opens the player when tapped.
• Propagated audiobook player timeline and playback-state changes to the notification lifecycle.

Validation

• GitHub Actions build-and-test passed for the notification fix.
• Focused JVM tests and debug APK assembly passed locally.
• The notification player was verified on Samsung SM-S931B, Android API 37, including opening the player from the notification.
• Extended background-playback validation for issue #379 remains requested from the affected reporter.

Reporter test request

Please install this prerelease, start a downloaded audiobook, switch to another app without swiping Lagrange away from Recents, and leave it backgrounded for several minutes. Please confirm whether audio continues playing and whether returning to Lagrange resumes at the expected position. Also confirm that the notification remains visible and opens the audiobook player when tapped.

This is a prerelease test build. Back up important data before testing.