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>

backend/internal/store/store_test.go

@@ -660,3 +660,104 @@ func TestDisplayChapter(t *testing.T) {
 		t.Errorf("DisplayLatest() = %q, want %q", got, "Ch 11")
 	}
 }
+
+func TestUpsertKindDefaultsToManga(t *testing.T) {
+	store := newTestStore(t)
+	got, err := store.Upsert(Bookmark{
+		Key: "asura:solo", Site: "asura", SeriesID: "solo", UpdatedAt: 1000,
+	})
+	if err != nil {
+		t.Fatalf("Upsert: %v", err)
+	}
+	if got.Kind != KindManga {
+		t.Fatalf("Kind = %q, want %q", got.Kind, KindManga)
+	}
+}
+
+func TestUpsertKindRoundTrips(t *testing.T) {
+	store := newTestStore(t)
+	got, err := store.Upsert(Bookmark{
+		Key: "lightnovelworld:a-will-eternal", Site: "lightnovelworld",
+		SeriesID: "a-will-eternal", Kind: KindNovel, UpdatedAt: 1000,
+	})
+	if err != nil {
+		t.Fatalf("Upsert: %v", err)
+	}
+	if got.Kind != KindNovel {
+		t.Fatalf("Kind = %q, want %q", got.Kind, KindNovel)
+	}
+}
+
+// The real hazard: a client that predates the column sends no kind at all. That
+// must keep the stored library, not silently demote a novel to manga.
+func TestUpsertEmptyKindKeepsStoredValue(t *testing.T) {
+	store := newTestStore(t)
+	if _, err := store.Upsert(Bookmark{
+		Key: "lightnovelworld:a-will-eternal", Site: "lightnovelworld",
+		SeriesID: "a-will-eternal", Kind: KindNovel, LastChapterNum: 10, UpdatedAt: 1000,
+	}); err != nil {
+		t.Fatalf("seed: %v", err)
+	}
+
+	got, err := store.Upsert(Bookmark{
+		Key: "lightnovelworld:a-will-eternal", Site: "lightnovelworld",
+		SeriesID: "a-will-eternal", Kind: "", LastChapterNum: 11, UpdatedAt: 2000,
+	})
+	if err != nil {
+		t.Fatalf("Upsert: %v", err)
+	}
+	if got.Kind != KindNovel {
+		t.Fatalf("Kind = %q, want %q — an empty kind must not reset the library", got.Kind, KindNovel)
+	}
+	if got.LastChapterNum != 11 {
+		t.Fatalf("LastChapterNum = %v, want 11 — progress in the same request must still land", got.LastChapterNum)
+	}
+}
+
+// A database created before this column exists must gain it, backfilled as
+// manga, without losing anything.
+func TestLegacyDatabaseGainsKindAsManga(t *testing.T) {
+	dbPath := filepath.Join(t.TempDir(), "legacy.db")
+
+	legacy, err := sql.Open("sqlite", dbPath)
+	if err != nil {
+		t.Fatalf("open legacy db: %v", err)
+	}
+	if _, err := legacy.Exec(`
+		CREATE TABLE bookmarks (
+		  key              TEXT PRIMARY KEY,
+		  site             TEXT NOT NULL,
+		  series_id        TEXT NOT NULL,
+		  title            TEXT,
+		  series_url       TEXT,
+		  cover            TEXT,
+		  last_chapter     TEXT,
+		  last_chapter_num REAL,
+		  last_chapter_url TEXT,
+		  updated_at       INTEGER NOT NULL
+		)`); err != nil {
+		t.Fatalf("create legacy schema: %v", err)
+	}
+	if _, err := legacy.Exec(`
+		INSERT INTO bookmarks (key, site, series_id, title, updated_at)
+		VALUES ('asura:legacy', 'asura', 'legacy', 'Legacy Series', 123)`); err != nil {
+		t.Fatalf("seed legacy row: %v", err)
+	}
+	if err := legacy.Close(); err != nil {
+		t.Fatalf("close legacy db: %v", err)
+	}
+
+	store, err := Open(dbPath)
+	if err != nil {
+		t.Fatalf("Open on legacy db: %v", err)
+	}
+	t.Cleanup(func() { store.Close() })
+
+	list, err := store.List()
+	if err != nil {
+		t.Fatalf("List: %v", err)
+	}
+	if len(list) != 1 || list[0].Kind != KindManga {
+		t.Fatalf("legacy row should backfill as manga, got %+v", list)
+	}
+}