feat(lyrics): prefetch on play + smooth measured-position autoscroll

Warm the lrclib cache the moment a track starts (Android PlayerController
onMediaItemTransition; web onNpSongChange) so opening the Lyrics tab is
instant. Extract a DOM-free fetch helper on web for reuse.

Rewrite Android lyrics autoscroll to center on the active line's measured
position in a LazyColumn instead of a fixed line-height estimate — removes
stutter and the downward drift on wrapped lines; active line sits at a
~40%-from-top reading anchor.

CHANGELOG: fold into 1.0; drop the now-fixed lyrics known-issue note.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -64,10 +64,12 @@ Versioning: two-part `MAJOR.MINOR` — each release bumps the minor (features an
 - **Android** — Offline playback: tap ▶ on a fully-downloaded group to play locally; downloaded songs are also served from disk automatically when opened from any album or playlist view
 - **Android** — Downloaded badge: albums and playlists in the Library tabs show a ↓-in-circle badge on the cover when fully downloaded
 - **Android** — Duplicate-safe storage: a song shared by an album and a playlist is stored once (keyed by song ID) and reference-counted on delete — removing one group keeps the file if another still needs it
+- **Web + Android** — Lyrics prefetch: lyrics are fetched the moment a track starts playing (not only when the Lyrics tab is opened), so opening Lyrics is instant. The lrclib cache is warmed on every song change
 
 ### Fixed
 - **Android** — Download crash on Android 15 (targetSdk 35): `FOREGROUND_SERVICE_TYPE_DATA_SYNC` is banned for apps targeting API 35; WorkManager's expedited path used it and the resulting exception killed the app ~1.5 s after tapping download. Fixed by dropping `setExpedited()` and all foreground-service use from `DownloadWorker` — downloads run as silent background work with progress shown in the Offline tab
 - **Android** — Offline detail screen flashed open then immediately returned: its initial empty state (before Room emitted) was mistaken for "deleted". Now shows a brief spinner until loaded, and only leaves when the last song is actually removed
+- **Android** — Lyrics autoscroll: rewrote centering to use the active line's *measured* position in a `LazyColumn` instead of a fixed line-height estimate. Eliminates the stutter and the downward drift on wrapped (multi-line) lyrics — the active line now tracks smoothly and sits at a natural ~40 %-from-top reading anchor
 
 ### Internal
 - **Android** — Offline system: `Room` DB (`novasonic_offline.db`) with `downloaded_tracks`, `download_groups`, `group_track_cross_refs`; `OfflineRepository` holds hot `StateFlow` maps for O(1) local-path lookups; `DownloadWorker` streams audio + cover art via `HttpURLConnection` to `context.filesDir/offline/{audio|covers}/`. `MusicRepository.streamUrl()` checks local files first, so playback uses the `file://` URI on every entry point