Make newsletter signup confirmation consistent and casual across all 4 forms

Same short "check your inbox" message everywhere instead of each form
having its own success wording (they'd drifted since each is a
separately-coded component, not a shared one).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/components/Newsletter.tsx

@@ -80,7 +80,7 @@ export function Newsletter({
           <div className="flex w-full md:flex-1 items-center md:self-stretch min-w-0">
             {status === "success" ? (
               <p className="text-body text-text-primary font-medium">
-                Danke! Du bist jetzt für den Newsletter angemeldet.
+                Fast geschafft! Schau kurz in dein Postfach – da wartet schon eine Mail von uns.
               </p>
             ) : (
               <form onSubmit={handleSubmit} className="flex flex-1 flex-col gap-4 min-w-0 w-full">