feat: unify authentication pages

apps/docs/docs/management/users/index.mdx

@@ -220,7 +220,8 @@ Clicking the `Copy & close` button will copy the URL to your clipboard.
 
 ### Self-onboarding
 
-Clicking the invitation link will bring up a form with fields for the username and password:
+Clicking the invitation link opens a centered registration form that uses the same visual shell as Homarr's onboarding
+and sign-in pages, with fields for the username and password:
 
 ![](./img/invitation-self-onboarding.png)