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/exec/tests/event_processor_with_json_output.rs

@@ -34,6 +34,7 @@ use codex_protocol::ThreadId;
 use codex_protocol::config_types::ModeKind;
 use codex_protocol::mcp::CallToolResult;
 use codex_protocol::models::WebSearchAction;
+use codex_protocol::openai_models::ReasoningEffort as ReasoningEffortConfig;
 use codex_protocol::plan_tool::PlanItemArg;
 use codex_protocol::plan_tool::StepStatus;
 use codex_protocol::plan_tool::UpdatePlanArgs;
@@ -547,6 +548,8 @@ fn collab_spawn_begin_and_end_emit_item_events() {
             call_id: "call-10".to_string(),
             sender_thread_id,
             prompt: prompt.clone(),
+            model: "gpt-5".to_string(),
+            reasoning_effort: ReasoningEffortConfig::default(),
         }),
     );
     let begin_events = ep.collect_thread_events(&begin);