fix(cover): restore full-resolution album and artist covers (#1205)

* fix(cover): build cover tiers from the full-resolution source

Derive the larger tiers from the decoded download instead of re-reading the just-written smaller tier (resize never upscales, so 512/800 were stored at the small resolution). Resolve the full-res 2000 tier exactly so it is actually downloaded and cached. Bump the cache layout stamp to drop already-poisoned tiers.

* fix(cover): open the cover lightbox at full resolution

Require the exact requested tier for the full-res helper so a smaller warmed tier no longer pins the lightbox to a downscaled image. Race the 2000 fetch against a 500ms opening window, show the 800 tier meanwhile, and persist 2000 for the next open. Adds an opening animation (reduced-motion aware) and tests.

* docs(changelog): note full-resolution cover fix (#1205)

* fix(cover): keep full-res peek exact in peek_batch and the grid seeder

Review follow-up: ensure-path peek alone left a hole — cover_cache_peek_batch still laddered a 2000 request down to a smaller tier, and the in-memory grid seeder wrote that smaller path under the 2000 key, so Hero/fullscreen/lightbox surfaces (which peek 2000 before ensure) still showed a downscaled cover. Share one exact-2000 rule (peek_plain_cover_tier) across ensure and peek_batch, and never seed the full-res key from a smaller tier file.

CHANGELOG.md

@@ -339,6 +339,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * History rows from other servers resolve album/cover metadata per server so Now Playing artwork loads when replaying cross-server plays.
 * Cross-server queue switches now send `playbackReport` **stopped** to the previous server so its Who is listening entry clears promptly.
 
+### Album and artist covers — full resolution restored
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#1205](https://github.com/Psychotoxical/psysonic/pull/1205)**
+
+* Album and artist covers — and the full-size view when you click a cover — could appear small and low-quality even though the source image was large, depending on how you reached the album. Root cause: the cache built its larger sizes from a smaller already-saved size instead of the full-resolution download, so they were stored downscaled. Covers are now built from the full-resolution image, and the full-size view opens at full resolution. The cover cache refreshes once on update. Reported by users on Discord.
+
 ## Under the Hood
 
 ### ESLint setup and a strict lint pass over the frontend