add route matcher to fix /login and /logout routes

Use SvelteKit param matcher to constrain [recipeLang] to only match
'recipes' or 'rezepte', preventing it from catching /login, /logout,
and other non-recipe routes.

src/routes/[recipeLang=recipeLang]/add/+page.server.ts

@@ -0,0 +1,13 @@
+import { redirect } from "@sveltejs/kit";
+
+export async function load({locals, params}) {
+    // Add is German-only - redirect to German version
+    if (params.recipeLang === 'recipes') {
+        throw redirect(301, '/rezepte/add');
+    }
+
+    const session = await locals.auth();
+    return {
+	user: session?.user
+    };
+};