Fix: Remove function prop from client component

Remove onSuccess callback from SyncRoyalMailButton since event handlers
cannot be passed to client components from server components. The button
already shows success/error messages, so the callback wasn't necessary.

src/components/SyncRoyalMailButton.tsx

@@ -5,10 +5,9 @@ import { useState } from 'react';
 interface SyncRoyalMailButtonProps {
   orderId: string;
   trackingNumber?: string | null;
-  onSuccess?: () => void;
 }
 
-export default function SyncRoyalMailButton({ orderId, trackingNumber, onSuccess }: SyncRoyalMailButtonProps) {
+export default function SyncRoyalMailButton({ orderId, trackingNumber }: SyncRoyalMailButtonProps) {
   const [loading, setLoading] = useState(false);
   const [message, setMessage] = useState<{ type: 'success' | 'error'; text: string } | null>(null);
 
@@ -37,8 +36,6 @@ export default function SyncRoyalMailButton({ orderId, trackingNumber, onSuccess
         type: 'success',
         text: `Tracking synced! Status: ${data.trackingData.status}`,
       });
-
-      onSuccess?.();
     } catch (err) {
       setMessage({ type: 'error', text: 'Error syncing with Royal Mail' });
     } finally {