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/login.html

@@ -194,7 +194,7 @@
             </div>
         </div>
         
-        <div class="auth-panel admin-setup-panel" id="admin-setup-panel">
+        <div class="auth-panel admin-setup-panel hidden" id="admin-setup-panel">
             <div class="auth-logo">
                 <div class="auth-logo-icon">
                     <svg viewBox="0 0 500 500">