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)

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 });
+};