rebrand: MangaBM → BookmarkManager, add novel library support (#15)

Two intertwined changes — the rebrand and the novel library were developed on
the same branch because the novel UI plumbing is part of the new "Bookmark
Manager" wordmark in the web shell.

## What it does

- **Rebrand**: MangaBM → BookmarkManager across the Go module, compose stack,
  env vars, Traefik hostnames, container/image names, userscript storage
  prefixes (`mangabm:cache` → `bmgr:manga:cache`, `mangabm:queue` → `bmgr:manga:queue`),
  and docs.
- **Novel library**: same backend, two libraries. New `kind` column splits
  bookmarks into `manga` / `novel`; PUT validates it. Two userscripts:
  - `manga-bookmark.user.js` — unchanged behaviour, just stamps its own `kind`.
  - `novel-bookmark.user.js` — separate Violentmonkey install with adapters
    for **novelfull.com** (polled via headless browser — Cloudflare JS
    challenge) and **lightnovelworld.net** (polled via plain TLS).
- **Web UI**: library switch on the app shell. Login art, libswitch, and
  novel-site colours from the Cinder design snapshot.

## Plumbing

- `addedColumns` ALTER for `kind` runs on first start after upgrade; every
  pre-existing row is backfilled to `'manga'`. No manual SQL, no down-time.
- `ALLOWED_ORIGINS` gains the two novel sites.
- New `NOVEL_USERSCRIPT_PATH` env (default `/userscript/novel-bookmark.user.js`),
  bindmounted alongside the manga script.
- Traefik router names `mangabm*` → `bmapi*` / `bmweb*`.

## Test status

- `go test ./...` — green
- `node --test userscript/test/logic.test.js` — 34 pass
- `node --test userscript/test/novel-logic.test.js` — 11 pass
- `node --check` on both userscripts — clean

## Notes for the redeploy

.env keys were renamed (`MANGA_API_HOST` → `BOOKMARK_API_HOST`,
`MANGA_WEB_HOST` → `BOOKMARK_WEB_HOST`). Update DNS / Traefik labels on the
prod override before pulling, otherwise the public hostnames go dark.
See the redeploy instructions I'll post next to this PR.

Reviewed-on: #15
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

.env.example

@@ -5,12 +5,13 @@
 API_TOKEN=changeme-generate-a-long-random-token
 
 # Comma-separated origins allowed to call the API (CORS). Both Asura domains
-# plus Demonic, Comix, and Kagane. Add/remove as the sites' hostnames change.
-ALLOWED_ORIGINS=https://asuracomic.net,https://asurascans.com,https://demonicscans.org,https://comix.to,https://kagane.to
+# plus Demonic, Comix, Kagane, and the two novel sites. Add/remove as the
+# sites' hostnames change.
+ALLOWED_ORIGINS=https://asuracomic.net,https://asurascans.com,https://demonicscans.org,https://comix.to,https://kagane.to,https://novelfull.com,https://lightnovelworld.net
 
 # --- Prod override (Traefik) only ---
 # Subdomain Traefik routes to this service (required by the prod override).
-# MANGA_API_HOST=manga-api.example.com
+# BOOKMARK_API_HOST=bookmark-api.example.com
 # Traefik's docker network name, if not "proxy".
 # PROXY_NETWORK=proxy
 # Traefik HTTPS entrypoint + cert resolver names, if yours differ from these.
@@ -18,7 +19,7 @@ ALLOWED_ORIGINS=https://asuracomic.net,https://asurascans.com,https://demonicsca
 # TRAEFIK_CERTRESOLVER=le
 
 # --- Web UI ---
-# Password for the browser UI at https://$MANGA_WEB_HOST. Leave unset to
+# Password for the browser UI at https://$BOOKMARK_WEB_HOST. Leave unset to
 # disable the web UI entirely (the routes are not registered at all).
 # Generate one: openssl rand -base64 18
 WEB_PASSWORD=
@@ -27,8 +28,8 @@ WEB_PASSWORD=
 # whether or not WEB_PASSWORD is set). Left commented on purpose: an example
 # value here would be a silent wrong-hostname fallback, and Traefik would
 # publish the UI router on a domain you do not own. The same container also
-# answers on MANGA_API_HOST for the userscript's API.
-# MANGA_WEB_HOST=manga.example.com
+# answers on BOOKMARK_API_HOST for the userscript's API.
+# BOOKMARK_WEB_HOST=bookmark.example.com
 
 # --- Latest-chapter poller ---
 # The backend re-checks each bookmarked series' newest published chapter on its