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.

.claude/settings.local.json

@@ -78,7 +78,8 @@
       "Bash(git commit -m 'Improve: Cart clearing on success page with better state management *)",
       "Bash(git commit -m 'Feature: Add order tracking and shipping status updates *)",
       "Bash(git commit -m 'Feature: Royal Mail tracking integration \\(hybrid approach\\) *)",
-      "Bash(git commit -m 'Fix: Refresh page after updating order tracking details *)"
+      "Bash(git commit -m 'Fix: Refresh page after updating order tracking details *)",
+      "Bash(git commit -m 'Fix: Remove function prop from client component *)"
     ]
   }
 }