Add resume_agent collab tool (#10903)

Summary
- add the new resume_agent collab tool path through core, protocol, and
the app server API, including the resume events
- update the schema/TypeScript definitions plus docs so resume_agent
appears in generated artifacts and README
- note that resumed agents rehydrate rollout history without overwriting
their base instructions

Testing
- Not run (not requested)

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -2500,6 +2500,7 @@ pub enum CommandExecutionStatus {
 pub enum CollabAgentTool {
     SpawnAgent,
     SendInput,
+    ResumeAgent,
     Wait,
     CloseAgent,
 }