build: publish mobile beta 1.9.0-beta.1

[Priveetee]

Summary

• Prepare beta version 1.9.0-beta.1 with version code 10824, moving the beta channel onto the 1.9 line.
• Sync beta with the development branch.
• Play YouTube lives from the server live manifest, fall back to the SABR route when the bootstrap cannot serve a video, and play Niconico and BiliBili provider media handles.
• Add previous and next video controls, and keep the favorite and watch later state synchronized with the library.
• Align the loading placeholders with the web client: card placeholders for the feeds, details placeholders for the player, and channel avatars that show a placeholder and retry before falling back to the initial.
• Enable bullet comments on BiliBili, and label scheduled lives as not started instead of reporting a delivery failure.
• Add subscription notifications that also run locally every fifteen minutes, including when UnifiedPush is registered.
• Fix a crash on Android 6.0 caused by the JVM URL encoder, and skip SABR prewarm for live videos.
• Publish the beta release body from release-notes when a matching note exists, so beta releases stop showing the merge commit message.

Verification

• 822 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, local notification delivery, and the new loading placeholders.
• API 37 runtime checks were blocked by the Android 17 emulator image itself; the APK is 16 KiB aligned and installs on the API 37 16 KiB image.