feat: add Environment admin UI page

SplitPane with create/edit/delete, production flag toggle,
enabled/disabled toggle. Follows existing admin page patterns.

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

ui/src/router.tsx

@@ -17,6 +17,7 @@ const AuditLogPage = lazy(() => import('./pages/Admin/AuditLogPage'));
 const OidcConfigPage = lazy(() => import('./pages/Admin/OidcConfigPage'));
 const DatabaseAdminPage = lazy(() => import('./pages/Admin/DatabaseAdminPage'));
 const ClickHouseAdminPage = lazy(() => import('./pages/Admin/ClickHouseAdminPage'));
+const EnvironmentsPage = lazy(() => import('./pages/Admin/EnvironmentsPage'));
 const AppConfigPage = lazy(() => import('./pages/Admin/AppConfigPage'));
 const LogsPage = lazy(() => import('./pages/LogsTab/LogsPage'));
 const SwaggerPage = lazy(() => import('./pages/Swagger/SwaggerPage'));
@@ -81,6 +82,7 @@ export const router = createBrowserRouter([
                 { path: 'oidc', element: <SuspenseWrapper><OidcConfigPage /></SuspenseWrapper> },
                 { path: 'database', element: <SuspenseWrapper><DatabaseAdminPage /></SuspenseWrapper> },
                 { path: 'clickhouse', element: <SuspenseWrapper><ClickHouseAdminPage /></SuspenseWrapper> },
+                { path: 'environments', element: <SuspenseWrapper><EnvironmentsPage /></SuspenseWrapper> },
               ],
             }],
           },