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>

README.md

@@ -86,7 +86,7 @@ curl -s -i -X OPTIONS -H 'Origin: https://asurascans.com' \
 
 ### Deploy behind your reverse proxy
 
-Route `https://manga-api.<domain>` → the service on `:8080` (TLS at the proxy).
+Route `https://bookmark-api.<domain>` → the service on `:8080` (TLS at the proxy).
 
 - **Host proxy** (nginx/Caddy on the host): the base compose already binds
   `127.0.0.1:8080`; point the proxy `proxy_pass http://127.0.0.1:8080;`.
@@ -99,7 +99,7 @@ Route `https://manga-api.<domain>` → the service on `:8080` (TLS at the proxy)
   ```
   Set `PROXY_NETWORK` in `.env` if your network isn't named `proxy`.
 
-Verify: `https://manga-api.<domain>/healthz` returns `ok` over valid TLS (no
+Verify: `https://bookmark-api.<domain>/healthz` returns `ok` over valid TLS (no
 mixed-content), and an `OPTIONS` preflight from a real site origin returns the
 CORS headers.
 
@@ -112,7 +112,7 @@ CORS headers.
 Edit the config block at the top of `userscript/manga-bookmark.user.js`:
 
 ```js
-const API_BASE = "https://manga-api.<domain>"; // no trailing slash
+const API_BASE = "https://bookmark-api.<domain>"; // no trailing slash
 const API_TOKEN = "<same token as backend>";
 ```
 
@@ -184,7 +184,7 @@ userscript does the looking, from your own browser session:
   (`LATEST_CHECK_BATCH` / `LATEST_CHECK_THROTTLE_MS`). Failures are silent and
   simply retried after the window.
 
-Freshness is tracked per device in `localStorage` under `mangabm:lastchecked`
+Freshness is tracked per device in `localStorage` under `bmgr:manga:lastchecked`
 and is deliberately not synced, since each device checks on its own.
 
 This means a bookmark is as current as its last check — not the moment a