feat: add AI Jobs admin page, cache model lists, improve image-gen 502 UX

- Add /admin/ai-jobs page with live-polling jobs table, status badges, progress bars, and cancel action
- Add listAIJobs() helper in pocketbase.ts; AIJob type
- Add POST /api/admin/ai-jobs/[id]/cancel SvelteKit proxy
- Add ai-jobs link to admin sidebar nav (all 5 locales)
- Cache image-gen and text-gen model lists in Valkey (10 min TTL) via scraper.ts helpers
- Cache changelog Gitea API response (5 min TTL)
- Improve 502/504 error message on image-gen page with CF AI timeout hint
- Show CF AI timeout warning in advanced options when a Cloudflare/FLUX model is selected

ui/src/routes/api/admin/ai-jobs/[id]/cancel/+server.ts

@@ -0,0 +1,29 @@
+/**
+ * POST /api/admin/ai-jobs/[id]/cancel
+ *
+ * Admin-only proxy to the Go backend's AI job cancel endpoint.
+ */
+
+import { json, error } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { log } from '$lib/server/logger';
+import { backendFetch } from '$lib/server/scraper';
+
+export const POST: RequestHandler = async ({ params, locals }) => {
+	if (!locals.user || locals.user.role !== 'admin') {
+		throw error(403, 'Forbidden');
+	}
+
+	const { id } = params;
+
+	let res: Response;
+	try {
+		res = await backendFetch(`/api/admin/ai-jobs/${id}/cancel`, { method: 'POST' });
+	} catch (e) {
+		log.error('admin/ai-jobs/cancel', 'backend proxy error', { id, err: String(e) });
+		throw error(502, 'Could not reach backend');
+	}
+
+	const data = await res.json().catch(() => ({}));
+	return json(data, { status: res.status });
+};