feat: make reasoning effort/summaries configurable (#1199)

Previous to this PR, we always set `reasoning` when making a request
using the Responses API:


d7245cbbc9/codex-rs/core/src/client.rs (L108-L111)

Though if you tried to use the Rust CLI with `--model gpt-4.1`, this
would fail with:

```shell
"Unsupported parameter: 'reasoning.effort' is not supported with this model."
```

We take a cue from the TypeScript CLI, which does a check on the model
name:


d7245cbbc9/codex-cli/src/utils/agent/agent-loop.ts (L786-L789)

This PR does a similar check, though also adds support for the following
config options:

```
model_reasoning_effort = "low" | "medium" | "high" | "none"
model_reasoning_summary = "auto" | "concise" | "detailed" | "none"
```

This way, if you have a model whose name happens to start with `"o"` (or
`"codex"`?), you can set these to `"none"` to explicitly disable
reasoning, if necessary. (That said, it seems unlikely anyone would use
the Responses API with non-OpenAI models, but we provide an escape
hatch, anyway.)

This PR also updates both the TUI and `codex exec` to show `reasoning
effort` and `reasoning summaries` in the header.

codex-rs/config.md

@@ -142,6 +142,34 @@ Users can specify config values at multiple levels. Order of precedence is as fo
 3. as an entry in `config.toml`, e.g., `model = "o3"`
 4. the default value that comes with Codex CLI (i.e., Codex CLI defaults to `codex-mini-latest`)
 
+## model_reasoning_effort
+
+If the model name starts with `"o"` (as in `"o3"` or `"o4-mini"`) or `"codex"`, reasoning is enabled by default when using the Responses API. As explained in the [OpenAI Platform documentation](https://platform.openai.com/docs/guides/reasoning?api-mode=responses#get-started-with-reasoning), this can be set to:
+
+- `"low"`
+- `"medium"` (default)
+- `"high"`
+
+To disable reasoning, set `model_reasoning_effort` to `"none"` in your config:
+
+```toml
+model_reasoning_effort = "none"  # disable reasoning
+```
+
+## model_reasoning_summary
+
+If the model name starts with `"o"` (as in `"o3"` or `"o4-mini"`) or `"codex"`, reasoning is enabled by default when using the Responses API. As explained in the [OpenAI Platform documentation](https://platform.openai.com/docs/guides/reasoning?api-mode=responses#reasoning-summaries), this can be set to:
+
+- `"auto"` (default)
+- `"concise"`
+- `"detailed"`
+
+To disable reasoning summaries, set `model_reasoning_summary` to `"none"` in your config:
+
+```toml
+model_reasoning_summary = "none"  # disable reasoning summaries
+```
+
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