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.

.dockerignore

@@ -0,0 +1,9 @@
+node_modules/
+build/
+.svelte-kit/
+.cache/
+.env
+.env.*
+*.log
+*.local
+.DS_Store