fix: Render ProfileModal in App.jsx and support guest display name editing from Navbar

frontend/src/App.jsx

@@ -651,6 +651,20 @@ export default function App() {
           onSubmit={handleGuestSubmit}
         />
       )}
+
+      {showProfileModal && (
+        <ProfileModal
+          user={user}
+          skills={skills}
+          onClose={() => setShowProfileModal(false)}
+          onUserUpdated={(updatedUser) => {
+            setUser(updatedUser);
+            setShowProfileModal(false);
+            refreshEvents();
+          }}
+          onRefreshSkills={refreshSkills}
+        />
+      )}
     </div>
   );
 }