Use model catalog default for reasoning summary fallback (#12873)

## Summary
- make `Config.model_reasoning_summary` optional so unset means use
model default
- resolve the optional config value to a concrete summary when building
`TurnContext`
- add protocol support for `default_reasoning_summary` in model metadata

## Validation
- `cargo test -p codex-core --lib client::tests -- --nocapture`

---------

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

codex-rs/tui/src/lib.rs

@@ -1159,7 +1159,9 @@ mod tests {
             personality: None,
             collaboration_mode: None,
             effort: config.model_reasoning_effort,
-            summary: config.model_reasoning_summary,
+            summary: config
+                .model_reasoning_summary
+                .unwrap_or(codex_protocol::config_types::ReasoningSummary::Auto),
             user_instructions: None,
             developer_instructions: None,
             final_output_json_schema: None,