[ios] Unable to submit prompt because button is hidden behind keyboard

<img width="359" height="638" alt="Image" src="https://github.com/user-attachments/assets/ed969b34-7de6-468a-99b9-9360687c62d9" />

Model: iPhone SE
IOS: 26.5

How to reproduce:

1. Start a new Codex chat inside an existing project with a git repo.
2. Start typing a prompt until the submit button moves behind the keyboard.
3. There is now way to press the submit button.