Codex Desktop: make high reasoning levels visually obvious

Problem

In Codex Desktop, the current reasoning-effort setting can be easy to miss after it has been
changed. This is especially risky for high and xhigh: those modes cost more and are most useful
when chosen intentionally, but the app does not make it visually obvious that a higher-cost mode is
active.

Request

Add a stronger visual treatment when the current thread is using higher reasoning effort, for
example:

• a subtle orange cast for high;
• a stronger red/orange cast for xhigh;
• a persistent tinted status/picker treatment anywhere the user can see the active model/effort.

The exact visual design can vary, but the important behavior is that a user glancing at the app can
tell when they are in a higher-cost reasoning mode without needing to reopen the picker or remember
what they selected earlier.

Why this matters

Higher reasoning settings are valuable when needed, but they should feel intentional. A persistent
visual signal would reduce accidental spend and make it clearer when the app is in a slower or more
expensive mode.

Edit: likely also applies to tui statusline