Tui: Rate limits (#3977)

### /limits: show rate limits graph

<img width="442" height="287" alt="image"
src="https://github.com/user-attachments/assets/3e29a241-a4b0-4df8-bf71-43dc4dd805ca"
/>

### Warning on close to rate limits:

<img width="507" height="96" alt="image"
src="https://github.com/user-attachments/assets/732a958b-d240-4a89-8289-caa92de83537"
/>

Based on #3965

codex-rs/tui/src/lib.rs

@@ -55,6 +55,7 @@ mod markdown_stream;
 mod new_model_popup;
 pub mod onboarding;
 mod pager_overlay;
+mod rate_limits_view;
 mod render;
 mod resume_picker;
 mod session_log;