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/+error.svelte

@@ -0,0 +1,27 @@
+<script lang="ts">
+  import { page } from '$app/stores';
+  import { useTranslate } from '$lib/translations';
+
+  const t = useTranslate();
+  const status = $derived($page.status);
+  const message = $derived($page.error?.message ?? '');
+</script>
+
+<svelte:head>
+  <title>{status === 404 ? t('page_404_title') : `Fehler ${status}`}</title>
+</svelte:head>
+
+<main class="mx-auto max-w-3xl px-4 py-12 text-center">
+  <h1 class="text-3xl font-bold text-zinc-900">{status}</h1>
+  {#if status === 404}
+    <p class="mt-2 text-zinc-600">{t('page_404_text')}</p>
+  {:else if message}
+    <p class="mt-2 text-zinc-600">{message}</p>
+  {/if}
+  <a
+    href="/"
+    class="mt-6 inline-block rounded bg-zinc-900 px-4 py-2 text-white hover:bg-zinc-800"
+  >
+    {t('page_404_back')}
+  </a>
+</main>