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>

graphify-out/.graphify_labels.json

@@ -15,8 +15,10 @@
   "13": "Web UI Handlers",
   "14": "Go Error Handling",
   "15": "CDP Browser Client",
+  "16": "Store",
   "17": "Go Code Style Guide",
   "18": "Agent Skills",
+  "19": "Open",
   "20": "I/O Performance Patterns",
   "21": "CPU Optimization",
   "22": "Caching Patterns",
@@ -35,6 +37,7 @@
   "35": "Web UI Filter Logic",
   "36": "Userscript Test Harness",
   "37": "Product & Security Context",
+  "38": "novel-logic.test.js",
   "39": "UI Critique 2026-07-26A",
   "40": "UI Critique 2026-07-26B",
   "41": "DB Cutover Runbook",
@@ -269,11 +272,5 @@
   "270": "Redeploy Runbook",
   "271": "Rollback Strategy",
   "272": "Bearer-token API client (apiGet/apiPut/apiDelete)",
-  "273": "Userscript AGENTS guidance",
-  "274": "manga-bookmark.user.js (single-IIFE manga script)",
-  "275": "novel-bookmark.user.js (novel script, bmgr:novel:)",
-  "276": "Offline retry queue (bmgr:manga:queue markers)",
-  "277": "Shadow DOM UI isolation from site CSS",
-  "278": "Site adapters (URL-regex detect, og:title)",
   "279": "Userscript CLAUDE guidance"
 }