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]/+page.svelte

@@ -0,0 +1,69 @@
+<script lang="ts">
+	import type { PageData } from './$types';
+    	import MediaScroller from '$lib/components/MediaScroller.svelte';
+    	import AddButton from '$lib/components/AddButton.svelte';
+    	import Card from '$lib/components/Card.svelte';
+    	import Search from '$lib/components/Search.svelte';
+    	let { data }: { data: PageData } = $props();
+    	let current_month = new Date().getMonth() + 1
+
+	const isEnglish = $derived(data.lang === 'en');
+	const categories = $derived(isEnglish
+		? ["Main Course", "Pasta", "Bread", "Dessert", "Soup", "Side Dish", "Salad", "Cake", "Breakfast", "Sauce", "Ingredient", "Drink", "Spread", "Cookie", "Snack"]
+		: ["Hauptspeise", "Nudel", "Brot", "Dessert", "Suppe", "Beilage", "Salat", "Kuchen", "Frühstück", "Sauce", "Zutat", "Getränk", "Aufstrich", "Guetzli", "Snack"]);
+
+	const labels = $derived({
+		title: isEnglish ? 'Recipes' : 'Rezepte',
+		subheading: isEnglish
+			? `${data.all_brief.length} recipes and constantly growing...`
+			: `${data.all_brief.length} Rezepte und stetig wachsend...`,
+		inSeason: isEnglish ? 'In Season' : 'In Saison',
+		metaTitle: isEnglish ? 'Bocken Recipes' : 'Bocken Rezepte',
+		metaDescription: isEnglish
+			? "A constantly growing collection of recipes from Bocken's kitchen."
+			: "Eine stetig wachsende Ansammlung an Rezepten aus der Bockenschen Küche.",
+		metaAlt: isEnglish ? 'Pasta al Ragu with Linguine' : 'Pasta al Ragu mit Linguine'
+	});
+</script>
+<style>
+h1{
+	text-align: center;
+	margin-bottom: 0;
+	font-size: 4rem;
+}
+.subheading{
+	text-align: center;
+	margin-top: 0;
+	font-size: 1.5rem;
+}
+</style>
+<svelte:head>
+	<title>{labels.metaTitle}</title>
+	<meta name="description" content="{labels.metaDescription}" />
+	<meta property="og:image" content="https://bocken.org/static/rezepte/thumb/ragu_aus_rindsrippen.webp" />
+	<meta property="og:image:secure_url" content="https://bocken.org/static/rezepte/thumb/ragu_aus_rindsrippen.webp" />
+	<meta property="og:image:type" content="image/webp" />
+	<meta property="og:image:alt" content="{labels.metaAlt}" />
+</svelte:head>
+
+<h1>{labels.title}</h1>
+<p class=subheading>{labels.subheading}</p>
+
+<Search></Search>
+
+<MediaScroller title={labels.inSeason}>
+{#each data.season as recipe}
+	<Card {recipe} {current_month} loading_strat={"eager"} do_margin_right={true} isFavorite={recipe.isFavorite} showFavoriteIndicator={!!data.session?.user} routePrefix="/{data.recipeLang}"></Card>
+{/each}
+</MediaScroller>
+
+{#each categories as category}
+	<MediaScroller title={category}>
+	{#each data.all_brief.filter(recipe => recipe.category == category) as recipe}
+		<Card {recipe} {current_month} do_margin_right={true} isFavorite={recipe.isFavorite} showFavoriteIndicator={!!data.session?.user} routePrefix="/{data.recipeLang}"></Card>
+	{/each}
+	</MediaScroller>
+{/each}
+{#if !isEnglish}
+	<AddButton href="/rezepte/add"></AddButton>
+{/if}