feat(user-settings): add user settings modal with username and password update

Implement user settings functionality in TopBar component with a modal dialog
that allows users to update their username and password. The modal includes
form validation and error handling, with proper password confirmation checks.

src/api/index.js

@@ -52,6 +52,8 @@ export const userApi = {
         api.post('/userMgr/remove', { targetUserID }),
     listUsers: () => 
         api.get('/userMgr/list'),
+    modifyUser: (userID, username, passwd) =>
+        api.post(`/userMgr/modify`, { userID, username, passwd }),
     modifyType: (userID, newType) =>
         api.post(`/userMgr/modifyType`, { userID, newType: newType.toLowerCase() || 'visitor' })
 };