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/lib/components/HeaderOverlay.svelte

@@ -0,0 +1,21 @@
+<script lang="ts">
+  import { get } from "svelte/store";
+  import { overlayOpen, overlayClose } from "$lib/overlay-store";
+  import { useTranslate } from "$lib/translations";
+  import { T } from "$lib/translations";
+
+  const t = useTranslate();
+
+  function handleClick() {
+    get(overlayClose)?.();
+  }
+</script>
+
+{#if $overlayOpen}
+  <button
+    type="button"
+    class="fixed inset-0 z-[15] bg-black/50 cursor-default"
+    aria-label={t(T.header_overlay_close)}
+    onclick={handleClick}
+  ></button>
+{/if}