Initial SvelteKit frontend port of windwiderstand.de

Full parity with Astro site: content rows, post/tag routes, pagination,
event badges + OSM map, comments, Live-Search via /api/search-index,
CMS image proxy, RSS, sitemap.

Deploy: Dockerfile + docker-compose.prod.yml + Gitea Actions workflow
to build + push to git.pm86.de registry and ssh-deploy to Contabo.

src/routes/robots.txt/+server.ts

@@ -0,0 +1,20 @@
+import type { RequestHandler } from './$types';
+import { env } from '$env/dynamic/public';
+
+export const GET: RequestHandler = ({ url }) => {
+  const base =
+    (env.PUBLIC_SITE_URL || url.origin).replace(/\/$/, '') || url.origin;
+  const body = [
+    'User-agent: *',
+    'Allow: /',
+    '',
+    `Sitemap: ${base}/sitemap.xml`,
+    '',
+  ].join('\n');
+  return new Response(body, {
+    headers: {
+      'Content-Type': 'text/plain; charset=utf-8',
+      'Cache-Control': 'public, max-age=3600',
+    },
+  });
+};