fix(css): increase login/register box width to 400px (#5963)

Wider box gives more room for form fields and improves readability.

Based on PR #5963 by @dfsmania.

Co-Authored-By: Diego Smania <diego.smania@gmail.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

dist/css/adminlte.css

@@ -26,7 +26,7 @@
 
 .login-box,
 .register-box {
-  width: 360px;
+  width: 400px;
 
   @media (max-width: map-get($grid-breakpoints, sm)) {
     width: 90%;