[config] Onboarding flow with persistence (#1929)

## Summary
In collaboration with @gpeal: upgrade the onboarding flow, and persist
user settings.

---------

Co-authored-by: Gabriel Peal <gabriel@openai.com>

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

@@ -1,5 +1,5 @@
 mod auth;
 mod continue_to_chat;
-mod git_warning;
 pub mod onboarding_screen;
+mod trust_directory;
 mod welcome;