feat: add CPU usage to agent response and compact cards

Backend:
- Add cpuUsage field to AgentInstanceResponse (-1 if unavailable)
- Add queryAgentCpuUsage() to AgentRegistrationController — queries
  avg CPU per instance from agent_metrics over last 2 minutes
- Wire CPU into agent list response via withCpuUsage()

Frontend:
- Add cpuUsage to schema.d.ts
- Compute maxCpu per AppGroup (max across all instances)
- Show "X% cpu" on compact cards when available (hidden when -1)

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

ui/src/api/schema.d.ts

@@ -2065,6 +2065,8 @@ export interface components {
             totalRoutes: number;
             /** Format: int64 */
             uptimeSeconds: number;
+            /** Format: double */
+            cpuUsage: number;
         };
         SseEmitter: {
             /** Format: int64 */

ui/src/pages/AgentHealth/AgentHealth.module.css

@@ -321,6 +321,11 @@
   color: var(--text-muted);
 }
 
+.compactCardCpu {
+  font-family: var(--font-mono);
+  color: var(--text-muted);
+}
+
 .compactCardHeartbeat {
   color: var(--text-muted);
 }

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -52,6 +52,7 @@ interface AppGroup {
   totalTps: number;
   totalActiveRoutes: number;
   totalRoutes: number;
+  maxCpu: number;
 }
 
 function groupByApp(agentList: AgentInstance[]): AppGroup[] {
@@ -71,6 +72,7 @@ function groupByApp(agentList: AgentInstance[]): AppGroup[] {
     totalTps: instances.reduce((s, i) => s + (i.tps ?? 0), 0),
     totalActiveRoutes: instances.reduce((s, i) => s + (i.activeRoutes ?? 0), 0),
     totalRoutes: instances.reduce((s, i) => s + (i.totalRoutes ?? 0), 0),
+    maxCpu: Math.max(...instances.map((i) => (i as AgentInstance & { cpuUsage?: number }).cpuUsage ?? -1)),
   }));
 }
 
@@ -141,6 +143,11 @@ function CompactAppCard({ group, onExpand, onNavigate }: { group: AppGroup; onEx
         <span className={styles.compactCardTps}>
           {group.totalTps.toFixed(1)} tps
         </span>
+        {group.maxCpu >= 0 && (
+          <span className={styles.compactCardCpu}>
+            {(group.maxCpu * 100).toFixed(0)}% cpu
+          </span>
+        )}
         <span className={isHealthy ? styles.compactCardHeartbeat : styles.compactCardHeartbeatWarn}>
           {heartbeat ? timeAgo(heartbeat) : '\u2014'}
         </span>