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]/season/[month]/+page.server.ts

@@ -0,0 +1,22 @@
+import type { PageServerLoad } from "./$types";
+import { getUserFavorites, addFavoriteStatusToRecipes } from "$lib/server/favorites";
+
+export const load: PageServerLoad = async ({ fetch, locals, params }) => {
+    const isEnglish = params.recipeLang === 'recipes';
+    const apiBase = isEnglish ? '/api/recipes' : '/api/rezepte';
+
+    const res_season = await fetch(`${apiBase}/items/in_season/` + params.month);
+    const item_season = await res_season.json();
+
+    // Get user favorites and session
+    const [userFavorites, session] = await Promise.all([
+        getUserFavorites(fetch, locals),
+        locals.auth()
+    ]);
+
+    return {
+        month: params.month,
+        season: addFavoriteStatusToRecipes(item_season, userFavorites),
+        session
+    };
+};

src/routes/[recipeLang]/season/[month]/+page.svelte

@@ -0,0 +1,23 @@
+<script lang="ts">
+    import type { PageData } from './$types';
+    import Recipes from '$lib/components/Recipes.svelte';
+    import SeasonLayout from '$lib/components/SeasonLayout.svelte';
+    import MediaScroller from '$lib/components/MediaScroller.svelte';
+    import Card from '$lib/components/Card.svelte';
+    import Search from '$lib/components/Search.svelte';
+    let { data }: { data: PageData } = $props();
+
+    const isEnglish = $derived(data.lang === 'en');
+    const months = $derived(isEnglish
+        ? ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]
+        : ["Januar", "Februar", "März", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember"]);
+
+    import { rand_array } from '$lib/js/randomize';
+</script>
+<SeasonLayout active_index={data.month -1} {months} routePrefix="/{data.recipeLang}">
+<Recipes slot=recipes>
+	{#each rand_array(data.season) as recipe}
+		<Card {recipe} icon_override=true isFavorite={recipe.isFavorite} showFavoriteIndicator={!!data.session?.user} routePrefix="/{data.recipeLang}"></Card>
+	{/each}
+</Recipes>
+</SeasonLayout>