refactor: enforce global Button component usage across all files (Header, Forms, Grids, MDX)

Former-commit-id: aa55620667a28e5c00ab2603da6ea6dc1e1c5ecf

components/forms/ContactForm.tsx

@@ -2,6 +2,7 @@
 
 import * as React from 'react';
 import { motion } from 'framer-motion';
+import { Button } from '@/components/ui/Button';
 
 export function ContactForm() {
   const [status, setStatus] = React.useState<'idle' | 'loading' | 'success' | 'error'>('idle');
@@ -99,10 +100,12 @@ export function ContactForm() {
             />
           </div>
 
-          <button 
+          <Button 
             type="submit" 
             disabled={status === 'loading'}
-            className="w-full bg-primary hover:bg-primary-dark text-white font-bold text-lg py-4 rounded-xl transition-all shadow-md hover:shadow-lg disabled:opacity-70 disabled:cursor-not-allowed flex items-center justify-center gap-2"
+            variant="primary"
+            size="lg"
+            className="w-full"
           >
             {status === 'loading' ? (
               <>
@@ -112,7 +115,7 @@ export function ContactForm() {
             ) : (
               'Nachricht absenden'
             )}
-          </button>
+          </Button>
           
           <p className="text-xs text-text-light text-center">
             Mit dem Absenden erkläre ich mich mit der Datenschutzerklärung einverstanden.