feat: admin Text Gen tool — chapter names + book description via CF Workers AI

Adds backend handlers and SvelteKit UI for an admin text generation tool.
The tool lets admins propose and apply AI-generated chapter titles and book
descriptions using Cloudflare Workers AI (12 LLM models, model selector shared
across both tabs).

ui/src/routes/admin/text-gen/+page.server.ts

@@ -0,0 +1,27 @@
+import type { PageServerLoad } from './$types';
+import { backendFetch } from '$lib/server/scraper';
+import { log } from '$lib/server/logger';
+
+export interface TextModelInfo {
+	id: string;
+	label: string;
+	provider: string;
+	context_size: number;
+	description: string;
+}
+
+export const load: PageServerLoad = async () => {
+	// Parent layout already guards admin role.
+	try {
+		const res = await backendFetch('/api/admin/text-gen/models');
+		if (!res.ok) {
+			log.warn('admin/text-gen', 'failed to load models', { status: res.status });
+			return { models: [] as TextModelInfo[] };
+		}
+		const data = await res.json();
+		return { models: (data.models ?? []) as TextModelInfo[] };
+	} catch (e) {
+		log.warn('admin/text-gen', 'backend unreachable', { err: String(e) });
+		return { models: [] as TextModelInfo[] };
+	}
+};