feat: admin UX overhaul — status filters, retry/cancel, mobile cards, i18n, shelf pre-populate

- Admin layout: SVG icons, active highlight, divider between nav sections
- Scrape page: status filter pills with counts, text + status combined search
- Audio page: status filter pills, cancel jobs, retry failed jobs, mobile cards for cache tab
- Translation page: status filter pills (incl. cancelled), cancel + retry jobs, mobile cancel/retry cards, i18n for all labels
- AI Jobs page: fix concurrent cancel (Set instead of single slot), per-job cancel errors inline, full mobile card layout, i18n title/heading
- Text-gen page: tagline editable input + copy, warnings copy, i18n title/heading
- Book page: chapter cover Save button, audio monitor link, currentShelf pre-populated from server
- pocketbase.ts: add getBookShelf(), shelf field on UserLibraryEntry
- New API route: POST /api/admin/translation/bulk (proxy for translation retry)
- i18n: 15 new admin_translation_*, admin_ai_jobs_*, admin_text_gen_* keys across all 5 locales

backend/internal/backend/handlers_image.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strconv"
 	"strings"
 	"time"
 
@@ -292,6 +293,129 @@ func sniffImageContentType(data []byte) string {
 	return "image/png"
 }
 
+// saveChapterImageRequest is the JSON body for POST /api/admin/image-gen/save-chapter-image.
+type saveChapterImageRequest struct {
+	// Slug is the book slug.
+	Slug string `json:"slug"`
+	// Chapter is the 1-based chapter number.
+	Chapter int `json:"chapter"`
+	// ImageB64 is the base64-encoded image bytes (PNG or JPEG).
+	ImageB64 string `json:"image_b64"`
+}
+
+// handleAdminImageGenSaveChapterImage handles POST /api/admin/image-gen/save-chapter-image.
+//
+// Accepts a pre-generated image as base64 and stores it as the chapter illustration
+// in MinIO, replacing the existing one if present. Does not call Cloudflare AI.
+func (s *Server) handleAdminImageGenSaveChapterImage(w http.ResponseWriter, r *http.Request) {
+	if s.deps.ChapterImageStore == nil {
+		jsonError(w, http.StatusServiceUnavailable, "chapter image store not configured")
+		return
+	}
+
+	var req saveChapterImageRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		jsonError(w, http.StatusBadRequest, "parse body: "+err.Error())
+		return
+	}
+	if req.Slug == "" {
+		jsonError(w, http.StatusBadRequest, "slug is required")
+		return
+	}
+	if req.Chapter <= 0 {
+		jsonError(w, http.StatusBadRequest, "chapter must be > 0")
+		return
+	}
+	if req.ImageB64 == "" {
+		jsonError(w, http.StatusBadRequest, "image_b64 is required")
+		return
+	}
+
+	imgData, err := base64.StdEncoding.DecodeString(req.ImageB64)
+	if err != nil {
+		imgData, err = base64.RawStdEncoding.DecodeString(req.ImageB64)
+		if err != nil {
+			jsonError(w, http.StatusBadRequest, "decode image_b64: "+err.Error())
+			return
+		}
+	}
+
+	contentType := sniffImageContentType(imgData)
+	if err := s.deps.ChapterImageStore.PutChapterImage(r.Context(), req.Slug, req.Chapter, imgData, contentType); err != nil {
+		s.deps.Log.Error("admin: save-chapter-image failed", "slug", req.Slug, "chapter", req.Chapter, "err", err)
+		jsonError(w, http.StatusInternalServerError, "save chapter image: "+err.Error())
+		return
+	}
+
+	s.deps.Log.Info("admin: chapter image saved", "slug", req.Slug, "chapter", req.Chapter, "bytes", len(imgData))
+	writeJSON(w, 0, map[string]any{
+		"saved":     true,
+		"image_url": fmt.Sprintf("/api/chapter-image/novelfire.net/%s/%d", req.Slug, req.Chapter),
+		"bytes":     len(imgData),
+	})
+}
+
+// handleHeadChapterImage handles HEAD /api/chapter-image/{domain}/{slug}/{n}.
+//
+// Returns 200 when an image exists for this chapter, 404 otherwise.
+// Used by the SSR loader to check existence without downloading the full image.
+func (s *Server) handleHeadChapterImage(w http.ResponseWriter, r *http.Request) {
+	if s.deps.ChapterImageStore == nil {
+		w.WriteHeader(http.StatusNotFound)
+		return
+	}
+
+	slug := r.PathValue("slug")
+	nStr := r.PathValue("n")
+	n, err := strconv.Atoi(nStr)
+	if err != nil || n <= 0 {
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	if s.deps.ChapterImageStore.ChapterImageExists(r.Context(), slug, n) {
+		w.WriteHeader(http.StatusOK)
+	} else {
+		w.WriteHeader(http.StatusNotFound)
+	}
+}
+
+// handleGetChapterImage handles GET /api/chapter-image/{domain}/{slug}/{n}.
+//
+// Serves the stored chapter illustration directly from MinIO.
+// Returns 404 when no image has been saved for this chapter.
+func (s *Server) handleGetChapterImage(w http.ResponseWriter, r *http.Request) {
+	if s.deps.ChapterImageStore == nil {
+		http.NotFound(w, r)
+		return
+	}
+
+	slug := r.PathValue("slug")
+	nStr := r.PathValue("n")
+	n, err := strconv.Atoi(nStr)
+	if err != nil || n <= 0 {
+		jsonError(w, http.StatusBadRequest, "invalid chapter number")
+		return
+	}
+
+	data, contentType, ok, err := s.deps.ChapterImageStore.GetChapterImage(r.Context(), slug, n)
+	if err != nil {
+		s.deps.Log.Error("chapter-image: get failed", "slug", slug, "n", n, "err", err)
+		jsonError(w, http.StatusInternalServerError, "could not retrieve chapter image")
+		return
+	}
+	if !ok {
+		http.NotFound(w, r)
+		return
+	}
+
+	w.Header().Set("Content-Type", contentType)
+	w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
+	w.Header().Set("Content-Length", fmt.Sprintf("%d", len(data)))
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write(data)
+}
+
 // handleAdminImageGenAsync handles POST /api/admin/image-gen/async.
 //
 // Fire-and-forget variant: validates the request, creates an ai_job record of

backend/internal/backend/server.go

@@ -57,6 +57,9 @@ type Dependencies struct {
 	// CoverStore reads and writes book cover images from MinIO.
 	// If nil, the cover endpoint falls back to a CDN redirect.
 	CoverStore bookstore.CoverStore
+	// ChapterImageStore reads and writes per-chapter illustration images from MinIO.
+	// If nil, chapter image endpoints return 404/503.
+	ChapterImageStore bookstore.ChapterImageStore
 	// Producer creates scrape/audio tasks in PocketBase.
 	Producer taskqueue.Producer
 	// TaskReader reads scrape/audio task records from PocketBase.
@@ -205,6 +208,11 @@ func (s *Server) ListenAndServe(ctx context.Context) error {
 	mux.HandleFunc("POST /api/admin/image-gen", s.handleAdminImageGen)
 	mux.HandleFunc("POST /api/admin/image-gen/async", s.handleAdminImageGenAsync)
 	mux.HandleFunc("POST /api/admin/image-gen/save-cover", s.handleAdminImageGenSaveCover)
+	mux.HandleFunc("POST /api/admin/image-gen/save-chapter-image", s.handleAdminImageGenSaveChapterImage)
+
+	// Chapter image serving
+	mux.HandleFunc("GET /api/chapter-image/{domain}/{slug}/{n}", s.handleGetChapterImage)
+	mux.HandleFunc("HEAD /api/chapter-image/{domain}/{slug}/{n}", s.handleHeadChapterImage)
 
 	// Admin text generation endpoints (chapter names + book description)
 	mux.HandleFunc("GET /api/admin/text-gen/models", s.handleAdminTextGenModels)