feat(subagents): add idle ttl cleanup and summary tool

README.md

@@ -804,12 +804,14 @@ Available tools:
 - `subagent.list` — list active child sessions
 - `subagent.cancel` — request cancellation for a running child turn
 - `subagent.delete` — remove a child session and clear its history
+- `subagent.summary` — inspect transcript summary for a child session
 
 Example flow:
 
 ```json
 {"name":"subagent.spawn","args":{"agent":"research","subagent_id":"plan-research","task":"Survey backup strategies for a 3-node homelab."}}
 {"name":"subagent.send","args":{"subagent_id":"plan-research","message":"Now compare operational risk and recovery-time tradeoffs."}}
+{"name":"subagent.summary","args":{"subagent_id":"plan-research","limit":20}}
 {"name":"subagent.list","args":{}}
 ```
 
@@ -820,6 +822,7 @@ agents:
   subagents:
     enabled: true
     max_active_sessions: 6
+    idle_ttl_ms: 3600000
 ```
 
 ## Running as Service