docs: drop the last references to cover scraping (#60)

Review follow-ups. The README's adapter reference and the userscript
testing skill still described a scrape that no longer exists, and the
manga test stub kept a querySelectorAll whose only caller was the
deleted coverFromPage. The handler comment's premise ("every installed
userscript still sends one") stops being true the moment a Reader
reinstalls, so it now says older copies may.

.claude/skills/testing-the-userscript/SKILL.md

@@ -14,7 +14,7 @@ parsers, helpers. UI, network, and storage behaviour are verified on-device.
 
 ```bash
 node --check userscript/manga-bookmark.user.js      # parse check, silent on success
-node --test userscript/test/logic.test.js           # 14 tests as of 2026-07-28
+node --test userscript/test/logic.test.js           # 35 tests as of 2026-08-10
 ```
 
 Run both before every commit that touches the userscript.

README.md

@@ -261,8 +261,10 @@ an API.
 
 ## Adapter reference (verified live 2026-07-24)
 
-The site adapters key everything off URL regex, with `title`/`cover` from
-`og:title` / `og:image`. Confirmed against live pages via Playwright:
+The site adapters key everything off URL regex, with `title` from `og:title`
+(or the page's own heading where a site ships none). No adapter reads a cover:
+the backend acquires, stores and serves every Cover from its own origin
+(ADR-0007). Confirmed against live pages via Playwright:
 
 | Site | Series URL | Chapter URL | `series_id` |
 |------|-----------|-------------|-------------|

backend/internal/api/handlers.go

@@ -51,11 +51,11 @@ func (h *Handler) Put(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	// A body may carry a cover, and it is discarded here rather than
-	// rejected: every installed userscript still sends one, and ADR-0004's
-	// compatibility argument depends on those scripts continuing to work. The
-	// Cover is acquired server-side (ADR-0007), so the field is permanently
-	// inert - not pending removal, and not a value any later code should
-	// start reading.
+	// rejected: an older installed userscript may still send one, and
+	// ADR-0004's compatibility argument depends on those scripts continuing
+	// to work. The Cover is acquired server-side (ADR-0007), so the field is
+	// permanently inert - not pending removal, and not a value any later code
+	// should start reading.
 	b.Cover = ""
 
 	// Path key is authoritative; derive site/series_id from it when the body

userscript/test/logic.test.js

@@ -41,9 +41,6 @@ globalThis.document = {
     const v = metaTags[m[1]];
     return v == null ? null : { getAttribute: () => v };
   },
-  querySelectorAll() {
-    return [];
-  },
   addEventListener() {},
   get title() {
     return docTitle;