refactor: unify recipe routes into [recipeLang] slug with full bilingual support

Consolidate /rezepte and /recipes routes into single [recipeLang] structure to eliminate code duplication. All pages now use conditional API routing and reactive labels based on language parameter.

- Merge duplicate route structures into /[recipeLang] with 404 for invalid slugs
- Add English API endpoints for search, favorites, tags, and categories
- Implement language dropdown in header with localStorage persistence
- Convert all pages to use Svelte 5 runes (, , )
- Add German-only redirects (301) for add/edit pages
- Make all view pages (list, detail, filters, search, favorites) fully bilingual
- Remove floating language switcher in favor of header dropdown

src/routes/[recipeLang]/category/+page.svelte

@@ -0,0 +1,27 @@
+<script lang="ts">
+    import type { PageData } from './$types';
+    import "$lib/css/nordtheme.css";
+    let { data }: { data: PageData } = $props();
+    import TagCloud from '$lib/components/TagCloud.svelte';
+    import TagBall from '$lib/components/TagBall.svelte';
+
+    const isEnglish = $derived(data.lang === 'en');
+    const labels = $derived({
+        title: isEnglish ? 'Categories' : 'Kategorien'
+    });
+</script>
+<style>
+	h1 {
+		text-align: center;
+		font-size: 3rem;
+	}
+</style>
+<h1>{labels.title}</h1>
+<section>
+<TagCloud>
+{#each data.categories as tag}
+	<TagBall {tag} ref="/{data.recipeLang}/category">
+	</TagBall>
+{/each}
+</TagCloud>
+</section>