feat: fetch server capabilities and hide infra tabs when disabled

Adds a useServerCapabilities hook that fetches /api/v1/health once per
session (staleTime: Infinity) and extracts the infrastructureEndpoints
flag. buildAdminTreeNodes now accepts an opts parameter so ClickHouse
and Database tabs are hidden when the server reports infra endpoints as
disabled. LayoutShell wires the hook result into the admin tree memo.

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

ui/src/components/LayoutShell.tsx

@@ -46,6 +46,7 @@ import {
   readCollapsed,
   writeCollapsed,
 } from './sidebar-utils';
+import { useServerCapabilities } from '../api/queries/capabilities';
 import type { SidebarApp } from './sidebar-utils';
 
 /* ------------------------------------------------------------------ */
@@ -290,6 +291,9 @@ function LayoutContent() {
   const globalFilters = useGlobalFilters();
   const { timeRange, autoRefresh, refreshTimeRange } = globalFilters;
 
+  // --- Server capabilities ------------------------------------------
+  const { data: capabilities } = useServerCapabilities();
+
   // --- Role checks ----------------------------------------------------
   const isAdmin = useIsAdmin();
 
@@ -432,8 +436,8 @@ function LayoutContent() {
   );
 
   const adminTreeNodes: SidebarTreeNode[] = useMemo(
-    () => buildAdminTreeNodes(),
-    [],
+    () => buildAdminTreeNodes({ infrastructureEndpoints: capabilities?.infrastructureEndpoints }),
+    [capabilities?.infrastructureEndpoints],
   );
 
   // --- Starred items ------------------------------------------------