feat(web): scroll-row arrows + stable desktop media tile

Home rows get hover left/right arrows that only show for the scrollable
direction (enhanceScrollRow + initScrollRows, called from startApp);
visibility recomputed on scroll/resize/content-load.

Fix the OS media tile flicker when skipping on desktop PWA: mutate the
existing MediaMetadata in place instead of assigning a new one each track
(the replacement made Windows tear down and rebuild the tile). Action
handlers are now set once.

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

CHANGELOG.md

@@ -67,12 +67,14 @@ Versioning: two-part `MAJOR.MINOR` — each release bumps the minor (features an
 - **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
 - **Web (PWA)** — Desktop install polish: `manifest.json` now ships PNG icons (192/512) for a crisp taskbar/Start-menu icon, drops the `portrait` lock so the window resizes freely, and adds a stable app `id` — installs as a standalone desktop window (no browser chrome)
 - **Web** — Keyboard shortcuts (desktop): Space = play/pause, ←/→ = seek 5 s, Shift+←/→ = previous/next track, ↑/↓ = volume. Ignored while typing in inputs/search fields
+- **Web** — Horizontal rows (Home) now have hover scroll arrows; only the scrollable direction is shown (no left arrow at the start, no right arrow at the end)
 
 ### 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
 - **Web** — Home now refreshes on an explicit Home click (matching Android): the album rows re-fetch and the random row re-randomizes instead of serving the 5-minute cache. Back/forward navigation still keeps the cached state
+- **Web (PWA)** — OS media tile no longer disappears/reappears when skipping tracks on desktop: the Media Session metadata is now mutated in place instead of replaced with a new `MediaMetadata` each track (which made Windows rebuild the tile)
 
 ### 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