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/params/recipeLang.ts

@@ -0,0 +1,5 @@
+import type { ParamMatcher } from '@sveltejs/kit';
+
+export const match: ParamMatcher = (param) => {
+	return param === 'recipes' || param === 'rezepte';
+};