Show spawned agent model and effort in TUI (#14273)

- include the requested sub-agent model and reasoning effort in the
spawn begin event\n- render that metadata next to the spawned agent name
and role in the TUI transcript

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/tools/handlers/multi_agents.rs

@@ -157,6 +157,8 @@ mod spawn {
                     call_id: call_id.clone(),
                     sender_thread_id: session.conversation_id,
                     prompt: prompt.clone(),
+                    model: args.model.clone().unwrap_or_default(),
+                    reasoning_effort: args.reasoning_effort.unwrap_or_default(),
                 }
                 .into(),
             )