feat: include reasoning_effort in NewConversationResponse (#3506)

`ClientRequest::NewConversation` picks up the reasoning level from the user's defaults in `config.toml`, so it should be reported in `NewConversationResponse`.

codex-rs/tui/src/chatwidget/tests.rs

@@ -138,6 +138,7 @@ fn resumed_initial_messages_render_history() {
     let configured = codex_core::protocol::SessionConfiguredEvent {
         session_id: conversation_id,
         model: "test-model".to_string(),
+        reasoning_effort: ReasoningEffortConfig::default(),
         history_log_id: 0,
         history_entry_count: 0,
         initial_messages: Some(vec![

codex-rs/tui/src/history_cell.rs

@@ -601,6 +601,7 @@ pub(crate) fn new_session_info(
 ) -> PlainHistoryCell {
     let SessionConfiguredEvent {
         model,
+        reasoning_effort: _,
         session_id: _,
         history_log_id: _,
         history_entry_count: _,