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/pages/AgentHealth/AgentHealth.tsx

@@ -189,7 +189,7 @@ export default function AgentHealth() {
 
   // Map events to FeedEvent
   const feedEvents: FeedEvent[] = useMemo(() => {
-    const mapped = (events ?? []).map((e: { id: number; agentId: string; eventType: string; detail: string; timestamp: string }) => ({
+    const mapped = (events ?? []).map((e: { id: number; instanceId: string; eventType: string; detail: string; timestamp: string }) => ({
       id: String(e.id),
       severity:
         e.eventType === 'WENT_DEAD'