fix(ui): resolve hidden class vs style.display conflict, polish toggle buttons

style.display='block'. All panel show/hide now uses classList.
- Fix admin badge/panel not showing in user menu (same root cause).
- Fix profile page main-content/auth-error panels (same root cause).
- Add hidden class to admin-setup-panel in login.html for consistency.
- Remove redundant .admin-setup-panel{display:none} CSS rule.
- Polish view toggle buttons: tighter gap, smaller size, subtler shadow.

static/css/views/auth.css

@@ -240,10 +240,7 @@
     display: none;
 }
 
-/* Admin setup panel styles */
-.admin-setup-panel {
-    display: none;
-}
+/* Admin setup panel styles — visibility controlled via .hidden class */
 
 .setup-steps {
     margin-bottom: 28px;