Support Built-in and Custom CLI Prompts in VS Code Extension via Slash Commands

What feature would you like to see?

Currently, in the Codex VS Code extension interface, using slash commands ("/") does nothing, whereas in the codex CLI, users can define both built-in and custom prompts accessible via the "/" command. It would be very helpful if the VS Code extension could support invoking these same built-in and custom prompts (defined for the CLI) directly from the extension UI using slash commands, providing parity and improving productivity.

Additional information

This request aims to unify the prompt handling experience across Codex CLI and VS Code extension, ensuring that custom and built-in prompts behave consistently and are accessible via "/" in both interfaces.