fix: cover_url bug, add save-cover endpoint, fix svelte-check CI failure

- Fix handlers_image.go: cover_url now uses /api/cover/novelfire.net/{slug} (was 'local')
- Add POST /api/admin/image-gen/save-cover: persists pre-generated base64 directly to
  MinIO via PutCover without re-calling Cloudflare AI
- Add SvelteKit proxy route api/admin/image-gen/save-cover/+server.ts
- Update UI saveAsCover(): send existing image_b64 to save-cover instead of re-generating
- Run npm run paraglide to compile admin_nav_image_gen message; force-add gitignored files
- svelte-check: 0 errors, 21 warnings (all pre-existing)

backend/internal/backend/handlers_image.go

@@ -195,7 +195,7 @@ func (s *Server) handleAdminImageGen(w http.ResponseWriter, r *http.Request) {
 			// Non-fatal: still return the image
 		} else {
 			saved = true
-			coverURL = fmt.Sprintf("/api/cover/local/%s", req.Slug)
+			coverURL = fmt.Sprintf("/api/cover/novelfire.net/%s", req.Slug)
 			s.deps.Log.Info("admin: generated cover saved", "slug", req.Slug, "bytes", len(imgData))
 		}
 	}
@@ -213,6 +213,62 @@ func (s *Server) handleAdminImageGen(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
+// saveCoverRequest is the JSON body for POST /api/admin/image-gen/save-cover.
+type saveCoverRequest struct {
+	// Slug is the book slug whose cover should be overwritten.
+	Slug string `json:"slug"`
+	// ImageB64 is the base64-encoded image bytes (PNG or JPEG).
+	ImageB64 string `json:"image_b64"`
+}
+
+// handleAdminImageGenSaveCover handles POST /api/admin/image-gen/save-cover.
+//
+// Accepts a pre-generated image as base64 and stores it as the book cover in
+// MinIO, replacing the existing one. Does not call Cloudflare AI at all.
+func (s *Server) handleAdminImageGenSaveCover(w http.ResponseWriter, r *http.Request) {
+	if s.deps.CoverStore == nil {
+		jsonError(w, http.StatusServiceUnavailable, "cover store not configured")
+		return
+	}
+
+	var req saveCoverRequest
+	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.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.CoverStore.PutCover(r.Context(), req.Slug, imgData, contentType); err != nil {
+		s.deps.Log.Error("admin: save-cover failed", "slug", req.Slug, "err", err)
+		jsonError(w, http.StatusInternalServerError, "save cover: "+err.Error())
+		return
+	}
+
+	s.deps.Log.Info("admin: cover saved via image-gen", "slug", req.Slug, "bytes", len(imgData))
+	writeJSON(w, 0, map[string]any{
+		"saved":     true,
+		"cover_url": fmt.Sprintf("/api/cover/novelfire.net/%s", req.Slug),
+		"bytes":     len(imgData),
+	})
+}
+
 // sniffImageContentType returns the MIME type of the image bytes.
 func sniffImageContentType(data []byte) string {
 	if len(data) >= 4 {

backend/internal/backend/server.go

@@ -189,6 +189,7 @@ func (s *Server) ListenAndServe(ctx context.Context) error {
 	// Admin image generation endpoints
 	mux.HandleFunc("GET /api/admin/image-gen/models", s.handleAdminImageGenModels)
 	mux.HandleFunc("POST /api/admin/image-gen", s.handleAdminImageGen)
+	mux.HandleFunc("POST /api/admin/image-gen/save-cover", s.handleAdminImageGenSaveCover)
 
 	// Voices list
 	mux.HandleFunc("GET /api/voices", s.handleVoices)

ui/src/lib/paraglide/messages/_index.js

@@ -333,6 +333,7 @@ export * from './admin_nav_scrape.js'
 export * from './admin_nav_audio.js'
 export * from './admin_nav_translation.js'
 export * from './admin_nav_changelog.js'
+export * from './admin_nav_image_gen.js'
 export * from './admin_nav_feedback.js'
 export * from './admin_nav_errors.js'
 export * from './admin_nav_analytics.js'

ui/src/lib/paraglide/messages/admin_nav_image_gen.js

@@ -0,0 +1,44 @@
+/* eslint-disable */
+import { getLocale, experimentalStaticLocale } from '../runtime.js';
+
+/** @typedef {import('../runtime.js').LocalizedString} LocalizedString */
+
+/** @typedef {{}} Admin_Nav_Image_GenInputs */
+
+const en_admin_nav_image_gen = /** @type {(inputs: Admin_Nav_Image_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Image Gen`)
+};
+
+const ru_admin_nav_image_gen = /** @type {(inputs: Admin_Nav_Image_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Image Gen`)
+};
+
+const id_admin_nav_image_gen = /** @type {(inputs: Admin_Nav_Image_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Image Gen`)
+};
+
+const pt_admin_nav_image_gen = /** @type {(inputs: Admin_Nav_Image_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Image Gen`)
+};
+
+const fr_admin_nav_image_gen = /** @type {(inputs: Admin_Nav_Image_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Image Gen`)
+};
+
+/**
+* | output |
+* | --- |
+* | "Image Gen" |
+*
+* @param {Admin_Nav_Image_GenInputs} inputs
+* @param {{ locale?: "en" | "ru" | "id" | "pt" | "fr" }} options
+* @returns {LocalizedString}
+*/
+export const admin_nav_image_gen = /** @type {((inputs?: Admin_Nav_Image_GenInputs, options?: { locale?: "en" | "ru" | "id" | "pt" | "fr" }) => LocalizedString) & import('../runtime.js').MessageMetadata<Admin_Nav_Image_GenInputs, { locale?: "en" | "ru" | "id" | "pt" | "fr" }, {}>} */ ((inputs = {}, options = {}) => {
+	const locale = experimentalStaticLocale ?? options.locale ?? getLocale()
+	if (locale === "en") return en_admin_nav_image_gen(inputs)
+	if (locale === "ru") return ru_admin_nav_image_gen(inputs)
+	if (locale === "id") return id_admin_nav_image_gen(inputs)
+	if (locale === "pt") return pt_admin_nav_image_gen(inputs)
+	return fr_admin_nav_image_gen(inputs)
+});

ui/src/routes/admin/image-gen/+page.svelte

@@ -219,28 +219,12 @@
 		saveSuccess = false;
 
 		try {
-			const payload = {
-				prompt: prompt.trim(),
-				model: result.model,
-				type: 'cover',
-				slug: result.slug,
-				num_steps: numSteps,
-				guidance,
-				strength,
-				width,
-				height,
-				save_to_cover: true
-			};
-
-			// Re-generate with save_to_cover=true (backend saves atomically)
-			// Alternatively, we could add a separate save endpoint.
-			// For now we pass the same prompt + model to re-generate and save.
-			// TODO: A lighter approach would be a dedicated save endpoint that accepts
-			// the base64 payload. For now re-gen is acceptable given admin-only usage.
-			const res = await fetch('/api/admin/image-gen', {
+			// Extract the raw base64 from the data URL (data:<mime>;base64,<b64>)
+			const b64 = result.imageSrc.split(',')[1];
+			const res = await fetch('/api/admin/image-gen/save-cover', {
 				method: 'POST',
 				headers: { 'Content-Type': 'application/json' },
-				body: JSON.stringify(payload)
+				body: JSON.stringify({ slug: result.slug, image_b64: b64 })
 			});
 			const body = await res.json().catch(() => ({}));
 			if (!res.ok) {

ui/src/routes/api/admin/image-gen/save-cover/+server.ts

@@ -0,0 +1,35 @@
+/**
+ * POST /api/admin/image-gen/save-cover
+ *
+ * Admin-only proxy: persists a pre-generated base64 image as a book cover in
+ * MinIO without re-calling Cloudflare AI.
+ *
+ * Body: { slug: string, image_b64: string }
+ */
+
+import { json, error } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { log } from '$lib/server/logger';
+import { backendFetch } from '$lib/server/scraper';
+
+export const POST: RequestHandler = async ({ request, locals }) => {
+	if (!locals.user || locals.user.role !== 'admin') {
+		throw error(403, 'Forbidden');
+	}
+
+	const body = await request.text();
+	let res: Response;
+	try {
+		res = await backendFetch('/api/admin/image-gen/save-cover', {
+			method: 'POST',
+			headers: { 'content-type': 'application/json' },
+			body
+		});
+	} catch (e) {
+		log.error('admin/image-gen/save-cover', 'backend proxy error', { err: String(e) });
+		throw error(502, 'Could not reach backend');
+	}
+
+	const data = await res.json().catch(() => ({}));
+	return json(data, { status: res.status });
+};