chore: rename codex-command to codex-shell-command (#11378)

This addresses some post-merge feedback on
https://github.com/openai/codex/pull/11361:

- crate rename
- reuse `detect_shell_type()` utility

codex-rs/shell-command/src/lib.rs

@@ -0,0 +1,11 @@
+//! Command parsing and safety utilities shared across Codex crates.
+
+mod shell_detect;
+
+pub mod bash;
+pub mod command_safety;
+pub mod parse_command;
+pub mod powershell;
+
+pub use command_safety::is_dangerous_command;
+pub use command_safety::is_safe_command;