build: publish mobile beta 1.8.1-beta.2

[Priveetee]

Summary

• Prepare beta version 1.8.1-beta.2 with version code 10823.
• Sync beta with the development branch.
• Include local subscription notifications, with a fifteen minute poll that keeps running even when UnifiedPush is registered, so a silent push no longer means no notification.
• Include YouTube live playback through the server live manifest, provider media handles for Niconico and Bilibili, the SABR bootstrap fallback, and typed provider errors.
• Enable bullet comments on Bilibili and label scheduled lives as not started instead of reporting a delivery failure.
• Fix a crash on Android 6.0 caused by the JVM URL encoder, and skip SABR prewarm for live videos.

Verification

• 817 unit tests passed with no failures.
• Lint passed, debug and release builds passed.
• Room migration and database instrumented tests: 18 passed on API 34, 10 passed on API 23, plus 8 tablet layout tests on a tablet AVD.
• Emulator checks on API 23 through API 36: install and launch on every level, YouTube VOD and live playback including a nine minute live soak with background transitions, Bilibili playback with bullet comments, Bilibili live playback, audio only mode, captions, sleep timer, next video advance, shorts, downloads sheet, picture in picture, search with service switching and search history, and local notification delivery.
• API 37 runtime checks were blocked by the Android 17 emulator image itself, which crashes surfaceflinger in mapper.ranchu.so; the APK is 16 KB aligned and installs on the API 37 16 KB image.