Greatest: serve catalog covers from a local copy (BL-0053)

The page hotlinked ~100 AniList CDN covers per load and some failed at random.
The reader now downloads each catalog cover once (sequential, ~1/s, stops on
401/403/429, images up to 2 MB) into data/greatest-covers/ and serves it from
/api/greatest-cover with a year-long browser cache; until a copy exists the
route redirects to the catalog URL. The page also accepts the server's
relative cover URLs, so owned titles show their library cover again.
GREATEST_COVER_WARM=0 turns the downloads off (tests, offline installs).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/greatest.md

@@ -23,7 +23,7 @@ Within each cohort, **Rank by my vote** sorts flame → good → neutral → sku
 
 The one-time seed is curated from the research document. All 106 catalog entries now have a cover URL. Most were matched to public AniList manga metadata; the five initial gaps were checked individually. Phoenix (1954) and Nausicaä use matching AniList records; Kitarō uses Drawn & Quarterly's Kitaro edition, Someone Hertz uses Shonen Jump's first-volume cover, and Hitoner uses Shueisha's 2026 first-volume cover. Hitoner's AniList 2024 entry represents an earlier work, so it was **not** used for the 2026 series. The five added URLs returned image content on 2026-10-09, but remote hosts can change them; the UI still shows a title-letter fallback if an image fails.
 
-`node tools/enrich-greatest-catalog.js` is an **optional manual** public-AniList metadata refresh, paced at one request every 1.5 seconds. It only accepts matching manga title and **original serialization year**, leaving uncertain results untouched rather than using a sequel or remake cover. The dashboard makes **no metadata calls when loading**; only an admin pressing **Search MangaDex** triggers a bounded lookup. Browser covers are lazy-loaded from their listed source; local library covers take precedence.
+`node tools/enrich-greatest-catalog.js` is an **optional manual** public-AniList metadata refresh, paced at one request every 1.5 seconds. It only accepts matching manga title and **original serialization year**, leaving uncertain results untouched rather than using a sequel or remake cover. The dashboard makes **no metadata calls when loading**; only an admin pressing **Search MangaDex** triggers a bounded lookup. Local library covers take precedence. For the rest, the reader keeps its own copy of each catalog cover in `data/greatest-covers/` (`greatest/covers.js`): it downloads missing ones one at a time, about one a second, 10 seconds after start and once a day, stops on HTTP 401/403/429, and accepts only JPEG/PNG/WebP/GIF/AVIF images up to 2 MB from the catalog's own HTTPS URLs. The page loads covers from `/api/greatest-cover`, which the browser caches for a year; until a copy exists that route redirects to the catalog URL. Hotlinking about 100 covers per page load made the image CDN drop some of them at random. `GREATEST_COVER_WARM=0` switches the downloads off.
 
 Public catalog chapter counts are often absent; the UI says “Chapters unknown” rather than inventing one. For owned titles, the local library count wins. Status comes from AniList's releasing/finished flag or local library metadata, and may be unknown. Official source links may be publisher editions, chapter services, or an award/info lead; they do not imply all chapters are available in every country. No unverified hoster coverage is claimed.