Remove the client latest-chapter scan for lightnovelworld (#91) (#93)

Follows the spec published on #91: remove the client-side latest-chapter scan for lightnovelworld rather than porting #87's truncation into a second codebase.

- lightnovelworld.latestChapterFromAnchors deleted, not stubbed: absence is what the background-fetch guard keys off.
- computeLatestChapter tolerates an adapter with no scanner (yields null) and is exported as the test seam.
- backgroundRefreshLatest skips a scanner-less Site before the due filter: no Series page fetched, no freshness timestamp recorded, no batch slot consumed. The on-page path (maybeCaptureLatestOnSeriesPage) routes through the same null-tolerant computation.
- novelfull's scanner, the shared max-chapter helper and all four manga Sites untouched.
- userscript/AGENTS.md records the Poll-only contract for this Site and why.

All seven acceptance criteria from the spec met. node --check clean; novel suite 30/30 (the regression pin fails if a lnw scan is reintroduced, scoped or not); manga suite 35/35, manga userscript byte-for-byte unchanged.

Two-axis code review: no hard standard violations, spec-clean; one follow-up commit matching the sibling adapter guard from the manga script.

Reviewed-on: #93
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

userscript/test/novel-logic.test.js

@@ -45,6 +45,7 @@ globalThis.document = {
 const {
   novelfull,
   lightnovelworld,
+  computeLatestChapter,
   kindOf,
   maxChapter,
   repairLnwStaleRow,
@@ -314,17 +315,40 @@ test("lightnovelworld.detect returns other for non-series paths", () => {
   assert.equal(lightnovelworld.detect(loc("https://lightnovelworld.net/az-lists/")).type, "other");
 });
 
-test("lightnovelworld.latestChapterFromAnchors takes the max and ignores other series", () => {
-  const best = lightnovelworld.latestChapterFromAnchors(
+test("computeLatestChapter yields nothing for lightnovelworld, comment anchors included", () => {
+  // A realistic Series-page anchor set: current-slug chapters, a second
+  // Chapter Slug's chapters, and a wpdiscuz comment pasting a high-numbered
+  // chapter of another novel (the poisoning vector). The client never scans
+  // this Site — the Poll's cooldown dominates the client throttle and the
+  // comment thread is a public write surface — so this must fail the moment
+  // a scan is reintroduced, scoped or not.
+  const latest = computeLatestChapter(
+    "lightnovelworld",
     [
       { href: "https://lightnovelworld.net/a-will-eternal-chapter-1/", text: "Chapter 1" },
       { href: "https://lightnovelworld.net/a-will-eternal-chapter-1317/", text: "Chapter 1317" },
       { href: "https://lightnovelworld.net/a-will-eternal-chapter-1298/", text: "Chapter 1298" },
+      // a divergent novel's second Chapter Slug
+      { href: "https://lightnovelworld.net/my-longevity-simulation-chapter-400/", text: "Chapter 400" },
+      // a wpdiscuz comment anchor
       { href: "https://lightnovelworld.net/overgeared-chapter-9999/", text: "Chapter 9999" },
     ],
     "a-will-eternal"
   );
-  assert.deepEqual(best, { num: 1317, label: "Chapter 1317" });
+  assert.equal(latest, null);
+});
+
+test("computeLatestChapter still scans novelfull and ignores other series", () => {
+  const best = computeLatestChapter(
+    "novelfull",
+    [
+      { href: "/reverend-insanity/chapter-2334-fang-yuan.html", text: "Chapter 2334" },
+      { href: "/reverend-insanity/chapter-1.html", text: "Chapter 1" },
+      { href: "/release-that-witch/chapter-9999.html", text: "Chapter 9999" },
+    ],
+    "reverend-insanity"
+  );
+  assert.deepEqual(best, { num: 2334, label: "Chapter 2334" });
 });
 
 test("latestChapterFromAnchors returns null when nothing matches", () => {