feat: add support for OpenAI tool type, local_shell (#961)

The new `codex-mini-latest` model expects a new tool with `{"type":
"local_shell"}`. Its contract is similar to the existing `function` tool
with `"name": "shell"`, so this takes the `local_shell` tool call into
`ExecParams` and sends it through the existing
`handle_container_exec_with_params()` code path.

This also adds the following logic when adding the default set of tools
to a request:

```rust
let default_tools = if self.model.starts_with("codex") {
    &DEFAULT_CODEX_MODEL_TOOLS
} else {
    &DEFAULT_TOOLS
};
```

That is, if the model name starts with `"codex"`, we add `{"type":
"local_shell"}` to the list of tools; otherwise, we add the
aforementioned `shell` tool.

To test this, I ran the TUI with `-m codex-mini-latest` and verified
that it used the `local_shell` tool. Though I also had some entries in
`[mcp_servers]` in my personal `config.toml`. The `codex-mini-latest`
model seemed eager to try the tools from the MCP servers first, so I
have personally commented them out for now, so keep an eye out if you're
testing `codex-mini-latest`!

Perhaps we should include more details with `{"type": "local_shell"}` or
update the following:


fd0b1b0208/codex-rs/core/prompt.md

For reference, the corresponding change in the TypeScript CLI is
https://github.com/openai/codex/pull/951.

codex-rs/core/src/rollout.rs

@@ -115,6 +115,7 @@ impl RolloutRecorder {
                 // "fully qualified MCP tool calls," so we could consider
                 // reformatting them in that case.
                 ResponseItem::Message { .. }
+                | ResponseItem::LocalShellCall { .. }
                 | ResponseItem::FunctionCall { .. }
                 | ResponseItem::FunctionCallOutput { .. } => {}
                 ResponseItem::Reasoning { .. } | ResponseItem::Other => {