Add reasoning-only status surface item (#25504)

Closes #24886.

## Why
Users can configure the TUI status line and terminal title with
`model-with-reasoning`, but issue #24886 asks for a compact
reasoning-only item. That lets a setup show just `default`, `low`,
`medium`, `high`, or `xhigh` without repeating the model name.

## What changed
- Added a `reasoning` item for `/statusline` and `/title` setup flows.
- Rendered the item from the effective reasoning effort, including
collaboration-mode overrides.
- Registered `reasoning` with `codex doctor` so Codex-generated
terminal-title config is not reported as invalid.
- Updated TUI setup snapshots so the picker previews include the new
item.

codex-rs/cli/src/doctor/title.rs

@@ -143,6 +143,7 @@ fn terminal_title_item_id(item: &str) -> Option<&'static str> {
         "fast-mode" => Some("fast-mode"),
         "model" | "model-name" => Some("model"),
         "model-with-reasoning" => Some("model-with-reasoning"),
+        "reasoning" => Some("reasoning"),
         "task-progress" => Some("task-progress"),
         _ => None,
     }