feat: add nick name to sub-agents (#12320)

Adding random nick name to sub-agents. Used for UX

At the same time, also storing and wiring the role of the sub-agent

codex-rs/core/tests/suite/sqlite_state.rs

@@ -123,6 +123,8 @@ async fn backfill_scans_existing_rollouts() -> Result<()> {
                     originator: "test".to_string(),
                     cli_version: "test".to_string(),
                     source: SessionSource::default(),
+                    agent_nickname: None,
+                    agent_role: None,
                     model_provider: None,
                     base_instructions: None,
                     dynamic_tools: Some(dynamic_tools_for_hook),