fix: improve ClickHouse admin page, fix AgentHealth type error

Rewrite ClickHouse admin to show useful storage metrics instead of
often-empty system.events data. Add active queries section.

- Replace performance endpoint: query system.parts for disk size,
  uncompressed size, compression ratio, total rows, part count
- Add /queries endpoint querying system.processes for active queries
- Frontend: storage overview strip, tables with total size, active
  queries DataTable
- Fix AgentHealth.tsx type: agentId → instanceId in inline type cast

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

ui/src/api/queries/admin/clickhouse.ts

@@ -21,11 +21,21 @@ export interface ClickHouseTableInfo {
 }
 
 export interface ClickHousePerformance {
-  queryCount: number;
-  insertQueryCount: number;
+  diskSize: string;
+  uncompressedSize: string;
+  compressionRatio: number;
+  totalRows: number;
+  partCount: number;
   memoryUsage: string;
-  insertedRows: number;
+  currentQueries: number;
+}
+
+export interface ClickHouseQuery {
+  queryId: string;
+  elapsedSeconds: number;
+  memory: string;
   readRows: number;
+  query: string;
 }
 
 export interface IndexerPipeline {
@@ -67,6 +77,15 @@ export function useClickHousePerformance() {
   });
 }
 
+export function useClickHouseQueries() {
+  const refetchInterval = useRefreshInterval(5_000);
+  return useQuery({
+    queryKey: ['admin', 'clickhouse', 'queries'],
+    queryFn: () => adminFetch<ClickHouseQuery[]>('/clickhouse/queries'),
+    refetchInterval,
+  });
+}
+
 export function useIndexerPipeline() {
   const refetchInterval = useRefreshInterval(10_000);
   return useQuery({