feat: include "reasoning" messages in Rust TUI (#892)

As shown in the screenshot, we now include reasoning messages from the
model in the TUI under the heading "codex reasoning":


![image](https://github.com/user-attachments/assets/d8eb3dc3-2f9f-4e95-847e-d24b421249a8)

To ensure these are visible by default when using `o4-mini`, this also
changes the default value for `summary` (formerly `generate_summary`,
which is deprecated in favor of `summary` according to the docs) from
unset to `"auto"`.

codex-rs/core/src/codex.rs

@@ -49,6 +49,7 @@ use crate::mcp_connection_manager::try_parse_fully_qualified_tool_name;
 use crate::mcp_tool_call::handle_mcp_tool_call;
 use crate::models::ContentItem;
 use crate::models::FunctionCallOutputPayload;
+use crate::models::ReasoningItemReasoningSummary;
 use crate::models::ResponseInputItem;
 use crate::models::ResponseItem;
 use crate::models::ShellToolCallParams;
@@ -934,6 +935,18 @@ async fn handle_response_item(
                 }
             }
         }
+        ResponseItem::Reasoning { id: _, summary } => {
+            for item in summary {
+                let text = match item {
+                    ReasoningItemReasoningSummary::SummaryText { text } => text,
+                };
+                let event = Event {
+                    id: sub_id.to_string(),
+                    msg: EventMsg::AgentReasoning { text },
+                };
+                sess.tx_event.send(event).await.ok();
+            }
+        }
         ResponseItem::FunctionCall {
             name,
             arguments,