Codex mobile expands reasoning traces by default; should match desktop collapsed behavior

Codex desktop keeps reasoning/thinking sections collapsed by default, with click-to-expand. That behavior is good.

On Codex mobile in the ChatGPT app, the full reasoning trace is expanded by default. For long high/xhigh Codex sessions, this makes the thread extremely hard to read and slows down review work.

Expected behavior:

• Keep reasoning collapsed by default on mobile, same as desktop.
• Allow tap-to-expand when I want to inspect it.
• Do not reduce reasoning effort or remove the trace; this is only a presentation issue.

This is especially important for users running high/xhigh reasoning, where the reasoning block can dominate the entire mobile screen.