Add legal link to TUI /plugin details (#15692)

- Adds language and "[learn
more](https://help.openai.com/en/articles/11487775-apps-in-chatgpt)"
link to plugin details pages.
-  Message is hidden when plugin is installed

<img width="1970" height="498" alt="image"
src="https://github.com/user-attachments/assets/f14330f7-661e-4860-8538-6dc9e8bbd90a"
/>

codex-rs/tui/src/onboarding/mod.rs

@@ -1,5 +1,6 @@
 mod auth;
 pub mod onboarding_screen;
 mod trust_directory;
+pub(crate) use auth::mark_url_hyperlink;
 pub use trust_directory::TrustDirectorySelection;
 mod welcome;