whitelist command prefix integration in core and tui (#7033)

this PR enables TUI to approve commands and add their prefixes to an
allowlist:
<img width="708" height="605" alt="Screenshot 2025-11-21 at 4 18 07 PM"
src="https://github.com/user-attachments/assets/56a19893-4553-4770-a881-becf79eeda32"
/>

note: we only show the option to whitelist the command when 
1) command is not multi-part (e.g `git add -A && git commit -m 'hello
world'`)
2) command is not already matched by an existing rule

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

@@ -570,6 +570,7 @@ mod tests {
             command: vec!["echo".into(), "ok".into()],
             reason: None,
             risk: None,
+            allow_prefix: None,
         }
     }