feat: add SvelteKit proxy route for admin dedup-chapters endpoint

ui/src/routes/api/admin/dedup-chapters/[slug]/+server.ts

@@ -0,0 +1,33 @@
+/**
+ * POST /api/admin/dedup-chapters/[slug]
+ *
+ * Admin-only proxy to the Go backend's dedup endpoint.
+ * Removes duplicate chapters_idx records for a book, keeping the latest
+ * record per chapter number. Returns { slug, deleted }.
+ */
+
+import { json, error } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { log } from '$lib/server/logger';
+import { backendFetch } from '$lib/server/scraper';
+
+export const POST: RequestHandler = async ({ params, locals }) => {
+	if (!locals.user || locals.user.role !== 'admin') {
+		throw error(403, 'Forbidden');
+	}
+
+	const { slug } = params;
+
+	let res: Response;
+	try {
+		res = await backendFetch(`/api/admin/dedup-chapters/${encodeURIComponent(slug)}`, {
+			method: 'POST'
+		});
+	} catch (e) {
+		log.error('admin/dedup-chapters', 'backend proxy error', { slug, err: String(e) });
+		throw error(502, 'Could not reach backend');
+	}
+
+	const data = await res.json().catch(() => ({}));
+	return json(data, { status: res.status });
+};