fix(home): Discover Songs covers for local-index tracks (#874)

* fix(home): pre-warm and prefetch Discover Songs row covers

The Discover Songs raблин. il came out of the cover pipeline merge with two
gaps that left its cards stuck on the placeholder disc icon on cold
caches.

- `warmHomeMainstageCovers` walked `heroAlbums` / `recent` / `random`
  through `ensureAlbumCoverMisses` + `predecodeWarmAlbums` but skipped
  `discoverSongs`, so songs that were peeked but missed on disk had to
  wait for lazy per-card ensure
- `Home.tsx`'s `coverPrefetchRegister` lumped `songRefs` into a
  `cappedRest` slice already saturated by 48 album refs + 16 artist
  refs at a 24-entry cap, so the song row's background prefetch was
  discarded entirely

Fix: ensure + decode-warm the Discover Songs cells alongside the album
rails, and register the song refs in their own bucket with a sane cap
and `middle` priority. Both follow the same shape as the working album
rails — no behavior change for surfaces that were already painting.

* fix(library): resolve track cover art from albumId for local index songs

Discover Songs uses runLocalRandomSongs; trackToSong only mapped coverArtId,
so rows with empty cover_art_id but a valid album_id showed the disc
placeholder. Mirror Rust COALESCE(cover_art_id, album_id) and Live Search's
coverArt ?? albumId in trackToSong, SongCard, and Home prefetch.

* docs(release): note Discover Songs cover fix in CHANGELOG and credits (PR #874)

* docs(release): credit PR #874 to Psychotoxical and cucadmuh jointly

* chore(credits): drop PR #874 from settingsCredits — minor fix

---------

Co-authored-by: Psychotoxical <171614930+Psychotoxical@users.noreply.github.com>

CHANGELOG.md

@@ -374,6 +374,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 
+### Home — Discover Songs cover art with local index
+
+**By [@Psychotoxical](https://github.com/Psychotoxical) + [@cucadmuh](https://github.com/cucadmuh), PR [#874](https://github.com/Psychotoxical/psysonic/pull/874)**
+
+* **Mainstage → Discover Songs** no longer shows disc placeholders when the local library index returns tracks without `coverArt` but with a valid `albumId` — cover resolution matches the Rust backfill rule (`COALESCE(cover_art_id, album_id)`).
+* Discover Songs row gets dedicated mainstage cover prefetch and warmup so song cards are not crowded out by album rails on cold caches.
+
+
+
 ## [1.46.0] - 2026-05-18
 
 > **🙏 Special thanks to [@zz5zz](https://github.com/zz5zz)** for his tireless quirk-spotting and bug reports on the [Psysonic Discord](https://discord.gg/AMnDRErm4u) — several of the polish fixes in this release landed directly off the back of his messages.