fix visual regressions in admin CSS refactor

Five missing line-height values caused pixel shifts when Tailwind
utilities (text-sm, text-lg, text-xs) were replaced with semantic
classes that only set font-size. Also remove phantom padding-bottom
on .admin-header (the old pb-4 utility was never defined).

Fixes: .admin-header, .admin-header-subtitle, .admin-error,
.admin-brand, .admin-text-secondary

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/css/admin.css

@@ -8,11 +8,9 @@
 @import "./theme-layer2-attributes.css";
 @import "./theme-semantic.css";
 
-/* Admin components, layout, icons, and transitions */
+/* Admin components, icons, and utilities */
 @import "./admin/components.css";
-@import "./admin/layout.css";
 @import "./admin/icons.css";
-@import "./admin/transitions.css";
 @import "./admin/utilities.css";
 
 /* LiveView loading state variants */