Fix/correct reasoning display (#6749)

This closes #6748 by implementing fallback to
`model_family.default_reasoning_effort` in `reasoning_effort` display of
`/status` when no `model_reasoning_effort` is set in the configuration.

## common/src/config_summary.rs

- `create_config_summary_entries` now fills the "reasoning effort" entry
with the explicit `config.model_reasoning_effort` when present and falls
back to `config.model_family.default_reasoning_effort` when it is
`None`, instead of emitting the literal string `none`.
- This ensures downstream consumers such as `tui/src/status/helpers.rs`
continue to work unchanged while automatically picking up model-family
defaults when the user has not selected a reasoning effort.

## tui/src/status/helpers.rs / core/src/model_family.rs

`ModelFamily::default_reasoning_effort` metadata is set to `medium` for
both `gpt-5*-codex` and `gpt-5` models following the default behaviour
of the API and recommendation of the codebase:
- per https://platform.openai.com/docs/api-reference/responses/create
`gpt-5` defaults to `medium` reasoning when no preset is passed
- there is no mention of the preset for `gpt-5.1-codex` in the API docs
but `medium` is the default setting for `gpt-5.1-codex` as per
`codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__model_reasoning_selection_popup.snap`

---------

Signed-off-by: lionelchg <[email protected]>
Co-authored-by: Eric Traut <[email protected]>

Author: lionelchg

codex-rs/common/src/config_summary.rs

@@ -15,13 +15,12 @@ pub fn create_config_summary_entries(config: &Config) -> Vec<(&'static str, Stri
     if config.model_provider.wire_api == WireApi::Responses
         && config.model_family.supports_reasoning_summaries
     {
-        entries.push((
-            "reasoning effort",
-            config
-                .model_reasoning_effort
-                .map(|effort| effort.to_string())
-                .unwrap_or_else(|| "none".to_string()),
-        ));
+        let reasoning_effort = config
+            .model_reasoning_effort
+            .or(config.model_family.default_reasoning_effort)
+            .map(|effort| effort.to_string())
+            .unwrap_or_else(|| "none".to_string());
+        entries.push(("reasoning effort", reasoning_effort));
         entries.push((
             "reasoning summaries",
             config.model_reasoning_summary.to_string(),