docs: propagate novel library + new sites into stale AGENTS.md top-matter

The rebrand (4229c17) rewrote root AGENTS.md as a compression pass and
switched Bromite->Violentmonkey, but the description still called the
project a manga-only tracker over two sites. Six sites, two libraries and
two userscripts now exist.

Root AGENTS.md:
- 'What this is' names both scripts and their sites, the kind column, and
  the <site>:<series_id> key shape.
- Origins constraint generalised past Asura/Demonic.
- Records that kagane and novelfull are reliably Cloudflare-challenged and
  browser-polled, which is the standing exception to the 'blocking is
  IP-reputation-based and not reproducible' note directly above it.
- Diagram says two userscripts.

backend/AGENTS.md:
- Store key list gained novelfull|lightnovelworld and the kind column.
- NOVEL_USERSCRIPT_PATH documented; it shipped in main.go:150 undocumented.

Child userscript/AGENTS.md already covered the novel adapters, so it is
untouched.

backend/AGENTS.md

@@ -11,7 +11,7 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   packages together into `newRouter`. Root-level `*_test.go` hold
   integration tests that exercise the full router; unit tests for a
   package live beside it under `internal/`.
-- **Single-user store.** One `bookmarks` table keyed `<site>:<series_id>` (`asura`|`demonic`|`comix`|`kagane`). Sync **last-write-wins**. Schema and endpoint list in plan.
+- **Single-user store.** One `bookmarks` table keyed `<site>:<series_id>` (`asura`|`demonic`|`comix`|`kagane`|`novelfull`|`lightnovelworld`), with a `kind` column (`manga`|`novel`) splitting the two libraries. Sync **last-write-wins**. Schema and endpoint list in plan.
 - **Endpoints:** `GET /bookmarks`, `PUT /bookmarks/{key}` (upsert; see `updated_at` rule below), `DELETE /bookmarks/{key}`, `GET /healthz` (no auth).
 - **Web UI:** same binary serve password-gated browser UI on second
   hostname — `GET /` (list, or login page when no session),
@@ -75,8 +75,10 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   (gates browser UI; unset disable it),
   `LATEST_CHAPTER_POLL_ENABLED`/`_COOLDOWN`/`_INTERVAL`/`_BATCH`/`_STAGGER`
   (background latest-chapter poller; defaults on, `1h`/`10m`/`14`/`20s`).
-  `USERSCRIPT_PATH` (file served at `/u/{token}/manga-bookmark.user.js`,
-  default `/userscript/manga-bookmark.user.js`, supplied by bindmount).
+  `USERSCRIPT_PATH` and `NOVEL_USERSCRIPT_PATH` (files served at
+  `/u/{token}/manga-bookmark.user.js` and `/u/{token}/novel-bookmark.user.js`,
+  defaults `/userscript/manga-bookmark.user.js` and
+  `/userscript/novel-bookmark.user.js`, both supplied by bindmount).
   `BROWSER_WS_URL` (headless-shell CDP endpoint for kagane and novelfull;
   unset disables browser polling and leaves those sites to the userscript
   alone).