feat: block explicit songs (#720)

[ZeroIndex-x636A06]

Closes #720

A smaller take on #780, as requested: no lyrics detection, just YouTube Music's explicit badge.

What it adds

• Block explicit songs setting (Android and desktop, off by default). When on, explicit songs are left out of AutoPlay and radio and skipped in the queue.
• Song rows and Home cards take an explicitBlocked parameter, true only while blocking is on and the song isn't allowed. A blocked one is greyed out, and tapping it asks: Allow this song, Turn off blocking, or Cancel. On Android the prompt uses the app's existing alert style.
• Allow this explicit song in the song menu does the same from there. The allowed list is a set of video ids in the existing settings, so Android backups include it.
• Home cards now carry the explicit badge from YouTube Music, so they show the E like other song rows.
• The desktop's own song lists (albums, playlists, an artist's top songs, History, Library, Downloads) show the E and are gated the same way.

The rule lives in shared/…/playback/ExplicitFilter.kt and the row helpers in sharedUi/…/components/ExplicitBlocked.kt (copied into desktopUi like the rest of the shared UI), so both apps share them. Rebased onto the current v1.8.1.

Testing

• New unit test ExplicitFilterTest passes.
• CI passes (Android, TV, desktop on Linux/macOS/Windows, backend) apart from LocaleStringsTest for zh-CN and zh-TW, which already fail on v1.8.1 (untranslated artist_signatures strings).
• Tested on Android and desktop (Linux): AutoPlay and radio, greyed rows and cards with the prompt, the E on Home and in the desktop's song lists, skipping in albums and playlists, and allowing and re-blocking a song.

Note: Just to be upfront, the code in this PR was generated with Claude, however I tested every feature by hand on both desktop (Linux) and mobile (Android) before submitting it. If anything looks off or you want something done differently, just let me know and I'll get it taken care of!