ux: improve admin header and drawer footer with meaningful information

- Enhanced topbar with better button styling and tooltips
- Added system information to drawer footer (server, update status)
- Improved visual hierarchy and spacing
- Better responsive design for mobile screens
- Replaced meaningless message with useful admin context

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

TaxBaik.Web/wwwroot/css/admin.css

@@ -1499,3 +1499,48 @@ textarea:focus-visible {
     transform: translateY(0);
   }
 }
+
+/* Improved Topbar & Navigation */
+.admin-topbar-actions {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+
+.admin-topbar-action {
+  white-space: nowrap;
+  font-size: 0.9rem;
+}
+
+/* Enhanced Drawer Footer */
+.admin-drawer-footer {
+  border-top: 1px solid var(--divider-color);
+  background: linear-gradient(180deg, transparent 0%, rgba(0,0,0,0.02) 100%);
+}
+
+.admin-footer-item {
+  display: flex;
+  align-items: center;
+  margin-bottom: 0.25rem;
+  color: var(--text-secondary);
+}
+
+.admin-footer-item .mud-icon {
+  color: var(--primary-color);
+}
+
+/* Responsive Topbar */
+@media (max-width: 600px) {
+  .admin-topbar-action {
+    padding: 4px 8px;
+    font-size: 0.8rem;
+  }
+
+  .admin-topbar-title {
+    min-width: 120px;
+  }
+
+  .mud-toolbar > :last-child {
+    margin-right: -8px;
+  }
+}