feat: admin soft-delete and hard-delete for books

- Add `archived` bool to domain.BookMeta, pbBook, and Meilisearch bookDoc
- ArchiveBook / UnarchiveBook patch the PocketBase record; ListBooks filters
  archived=false so hidden books disappear from all public responses
- Meilisearch: add `archived` as a filterable attribute; Search and Catalogue
  always prepend `archived = false` to exclude archived books from results
- DeleteBook permanently removes the PocketBase record, all chapters_idx rows,
  MinIO chapter objects, cover image, and the Meilisearch document
- New BookAdminStore interface with ArchiveBook, UnarchiveBook, DeleteBook
- Admin HTTP endpoints: PATCH /api/admin/books/{slug}/archive|unarchive,
  DELETE /api/admin/books/{slug}
- PocketBase schema: archived field added to live pb.libnovel.cc and to
  pb-init-v3.sh (both create block and add_field migration)

backend/internal/storage/store.go

@@ -55,6 +55,7 @@ var _ bookstore.CoverStore = (*Store)(nil)
 var _ bookstore.TranslationStore = (*Store)(nil)
 var _ bookstore.AIJobStore = (*Store)(nil)
 var _ bookstore.ChapterImageStore = (*Store)(nil)
+var _ bookstore.BookAdminStore = (*Store)(nil)
 var _ taskqueue.Producer = (*Store)(nil)
 var _ taskqueue.Consumer = (*Store)(nil)
 var _ taskqueue.Reader = (*Store)(nil)
@@ -226,6 +227,7 @@ type pbBook struct {
 	Ranking       int      `json:"ranking"`
 	Rating        float64  `json:"rating"`
 	Updated       string   `json:"updated"`
+	Archived      bool     `json:"archived"`
 }
 
 func (b pbBook) toDomain() domain.BookMeta {
@@ -246,6 +248,7 @@ func (b pbBook) toDomain() domain.BookMeta {
 		Ranking:       b.Ranking,
 		Rating:        b.Rating,
 		MetaUpdated:   metaUpdated,
+		Archived:      b.Archived,
 	}
 }
 
@@ -275,7 +278,7 @@ func (s *Store) ReadMetadata(ctx context.Context, slug string) (domain.BookMeta,
 }
 
 func (s *Store) ListBooks(ctx context.Context) ([]domain.BookMeta, error) {
-	items, err := s.pb.listAll(ctx, "books", "", "title")
+	items, err := s.pb.listAll(ctx, "books", "archived=false", "title")
 	if err != nil {
 		return nil, err
 	}
@@ -376,6 +379,84 @@ func (s *Store) ReindexChapters(ctx context.Context, slug string) (int, error) {
 	return count, nil
 }
 
+// ── BookAdminStore ────────────────────────────────────────────────────────────
+
+// ArchiveBook sets archived=true on the book record for slug.
+func (s *Store) ArchiveBook(ctx context.Context, slug string) error {
+	book, err := s.getBookBySlug(ctx, slug)
+	if err == ErrNotFound {
+		return ErrNotFound
+	}
+	if err != nil {
+		return fmt.Errorf("ArchiveBook: %w", err)
+	}
+	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/books/records/%s", book.ID),
+		map[string]any{"archived": true})
+}
+
+// UnarchiveBook clears archived on the book record for slug.
+func (s *Store) UnarchiveBook(ctx context.Context, slug string) error {
+	book, err := s.getBookBySlug(ctx, slug)
+	if err == ErrNotFound {
+		return ErrNotFound
+	}
+	if err != nil {
+		return fmt.Errorf("UnarchiveBook: %w", err)
+	}
+	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/books/records/%s", book.ID),
+		map[string]any{"archived": false})
+}
+
+// DeleteBook permanently removes all data for a book:
+//   - PocketBase books record
+//   - All PocketBase chapters_idx records for the slug
+//   - All MinIO chapter markdown objects ({slug}/chapter-*.md)
+//   - MinIO cover image (covers/{slug}.jpg)
+func (s *Store) DeleteBook(ctx context.Context, slug string) error {
+	// 1. Fetch the book record to get its PocketBase ID.
+	book, err := s.getBookBySlug(ctx, slug)
+	if err == ErrNotFound {
+		return ErrNotFound
+	}
+	if err != nil {
+		return fmt.Errorf("DeleteBook: fetch: %w", err)
+	}
+
+	// 2. Delete all chapters_idx records.
+	filter := fmt.Sprintf(`slug=%q`, slug)
+	items, err := s.pb.listAll(ctx, "chapters_idx", filter, "")
+	if err != nil && err != ErrNotFound {
+		return fmt.Errorf("DeleteBook: list chapters_idx: %w", err)
+	}
+	for _, raw := range items {
+		var rec struct {
+			ID string `json:"id"`
+		}
+		if json.Unmarshal(raw, &rec) == nil && rec.ID != "" {
+			if delErr := s.pb.delete(ctx, fmt.Sprintf("/api/collections/chapters_idx/records/%s", rec.ID)); delErr != nil {
+				s.log.Warn("DeleteBook: delete chapters_idx record failed", "slug", slug, "id", rec.ID, "err", delErr)
+			}
+		}
+	}
+
+	// 3. Delete MinIO chapter objects.
+	if err := s.mc.deleteObjects(ctx, s.mc.bucketChapters, slug+"/"); err != nil {
+		s.log.Warn("DeleteBook: delete chapter objects failed", "slug", slug, "err", err)
+	}
+
+	// 4. Delete MinIO cover image.
+	if err := s.mc.deleteObjects(ctx, s.mc.bucketBrowse, CoverObjectKey(slug)); err != nil {
+		s.log.Warn("DeleteBook: delete cover failed", "slug", slug, "err", err)
+	}
+
+	// 5. Delete the PocketBase books record.
+	if err := s.pb.delete(ctx, fmt.Sprintf("/api/collections/books/records/%s", book.ID)); err != nil {
+		return fmt.Errorf("DeleteBook: delete books record: %w", err)
+	}
+
+	return nil
+}
+
 // ── RankingStore ──────────────────────────────────────────────────────────────
 
 func (s *Store) WriteRankingItem(ctx context.Context, item domain.RankingItem) error {