feat: add RBAC management UI with dashboard, users, groups, and roles tabs

Tab-based admin page at /admin/rbac with split-pane entity views,
inheritance visualization, OIDC badges, and role/group management.

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

ui/src/router.tsx

@@ -13,6 +13,7 @@ const SwaggerPage = lazy(() => import('./pages/swagger/SwaggerPage').then(m => (
 const DatabaseAdminPage = lazy(() => import('./pages/admin/DatabaseAdminPage').then(m => ({ default: m.DatabaseAdminPage })));
 const OpenSearchAdminPage = lazy(() => import('./pages/admin/OpenSearchAdminPage').then(m => ({ default: m.OpenSearchAdminPage })));
 const AuditLogPage = lazy(() => import('./pages/admin/AuditLogPage').then(m => ({ default: m.AuditLogPage })));
+const RbacPage = lazy(() => import('./pages/admin/rbac/RbacPage').then(m => ({ default: m.RbacPage })));
 
 export const router = createBrowserRouter([
   {
@@ -38,6 +39,7 @@ export const router = createBrowserRouter([
           { path: 'admin/opensearch', element: <Suspense fallback={null}><OpenSearchAdminPage /></Suspense> },
           { path: 'admin/audit', element: <Suspense fallback={null}><AuditLogPage /></Suspense> },
           { path: 'admin/oidc', element: <OidcAdminPage /> },
+          { path: 'admin/rbac', element: <Suspense fallback={null}><RbacPage /></Suspense> },
           { path: 'swagger', element: <Suspense fallback={null}><SwaggerPage /></Suspense> },
         ],
       },