fix(ui): install prod deps in Docker runtime; add reindex endpoint for chapters_idx

- ui/Dockerfile: copy package-lock.json and run npm ci --omit=dev in the
  runtime stage so marked (and other runtime deps) are available to
  adapter-node at startup — fixes ERR_MODULE_NOT_FOUND for 'marked'
- storage: add ReindexChapters to Store interface and HybridStore — walks
  MinIO objects for a slug, reads chapter titles, upserts chapters_idx
- server: add POST /api/reindex/{slug} to rebuild chapters_idx from MinIO

scraper/internal/server/server.go

@@ -126,6 +126,8 @@ func (s *Server) ListenAndServe(ctx context.Context) error {
 	// Scrape status
 	mux.HandleFunc("GET /api/scrape/status", s.handleScrapeStatus)
 	mux.HandleFunc("GET /api/scrape/tasks", s.handleScrapeTasks)
+	// Re-index chapters for a book from MinIO into PocketBase chapters_idx
+	mux.HandleFunc("POST /api/reindex/{slug}", s.handleReindex)
 	// Progress API
 	mux.HandleFunc("GET /api/progress", s.handleGetProgress)
 	mux.HandleFunc("POST /api/progress/{slug}", s.handleSetProgress)
@@ -1067,3 +1069,43 @@ func (s *Server) handleScrapeTasks(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json")
 	_ = json.NewEncoder(w).Encode(tasks)
 }
+
+// handleReindex handles POST /api/reindex/{slug}.
+// It rebuilds the chapters_idx PocketBase collection for the given book by
+// walking its MinIO objects. Use this when chapters were scraped but the index
+// is out of sync (e.g. after a failed UpsertChapterIdx during scraping).
+func (s *Server) handleReindex(w http.ResponseWriter, r *http.Request) {
+	slug := r.PathValue("slug")
+	if slug == "" {
+		http.Error(w, `{"error":"missing slug"}`, http.StatusBadRequest)
+		return
+	}
+
+	type reindexer interface {
+		ReindexChapters(ctx context.Context, slug string) (int, error)
+	}
+	ri, ok := s.store.(reindexer)
+	if !ok {
+		http.Error(w, `{"error":"store does not support reindex"}`, http.StatusNotImplemented)
+		return
+	}
+
+	count, err := ri.ReindexChapters(r.Context(), slug)
+	if err != nil {
+		s.log.Error("reindex failed", "slug", slug, "indexed", count, "err", err)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusInternalServerError)
+		_ = json.NewEncoder(w).Encode(map[string]interface{}{
+			"error":   err.Error(),
+			"indexed": count,
+		})
+		return
+	}
+
+	s.log.Info("reindex complete", "slug", slug, "indexed", count)
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(map[string]interface{}{
+		"slug":    slug,
+		"indexed": count,
+	})
+}