fix(#112): remove dead admin breadcrumb code, add logout aria-label

Review feedback: breadcrumb memo had an unused isAdminPage branch
(TopBar no longer renders on admin pages). Added aria-label to
icon-only logout button for screen readers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/LayoutShell.tsx

@@ -203,23 +203,6 @@ function LayoutContent() {
 
   const isAdminPage = location.pathname.startsWith('/admin');
   const breadcrumb = useMemo(() => {
-    if (isAdminPage) {
-      const LABELS: Record<string, string> = {
-        admin: 'Admin',
-        rbac: 'Users & Roles',
-        audit: 'Audit Log',
-        oidc: 'OIDC',
-        database: 'Database',
-        clickhouse: 'ClickHouse',
-        appconfig: 'App Config',
-      };
-      const parts = location.pathname.split('/').filter(Boolean);
-      return parts.map((part, i) => ({
-        label: LABELS[part] ?? part,
-        ...(i < parts.length - 1 ? { href: '/' + parts.slice(0, i + 1).join('/') } : {}),
-      }));
-    }
-    // Scope trail as breadcrumb items
     const items: { label: string; href?: string }[] = [
       { label: 'All Applications', href: `/${scope.tab}` },
     ];
@@ -234,7 +217,7 @@ function LayoutContent() {
       delete items[items.length - 1].href;
     }
     return items;
-  }, [location.pathname, isAdminPage, scope.tab, scope.appId, scope.routeId]);
+  }, [scope.tab, scope.appId, scope.routeId]);
 
   const handleLogout = useCallback(() => {
     logout();