Add Turnstile protection to user actions

app/(frontend)/registrieren/page.tsx

@@ -7,6 +7,7 @@ import { RegisterForm } from "@/components/auth/RegisterForm";
 import { getCurrentCustomer } from "@/lib/auth/customer";
 
 export const dynamic = "force-dynamic";
+const turnstileSiteKey = process.env.TURNSTILE_SITE_KEY ?? "";
 
 export const metadata: Metadata = {
   title: "Konto erstellen",
@@ -28,7 +29,7 @@ export default async function RegisterPage() {
       />
       <Section tone="plain">
         <div className="mx-auto max-w-md">
-          <RegisterForm />
+          <RegisterForm siteKey={turnstileSiteKey} />
           <p className="mt-6 text-center text-sm text-anouma-plum">
             Schon ein Konto?{" "}
             <Link href="/login" className="font-medium text-anouma-mauve-dark underline underline-offset-4">