[FEATURE] Allow disabling built-in skills via config.toml

What feature would you like to see?

A setting in config.toml to disable built-in skills (e.g. Skill Creator).

Currently, there is no way to opt out of built-in skills that ship with Codex. If a user has their own custom skill that covers the same domain (e.g. a custom skill creator), the built-in one still gets loaded and competes for activation, wasting context and sometimes triggering instead of the user's preferred skill.

A config.toml option like this would solve it:

[[skills.config]]
name = "Skill Creator"
enabled = false

Or alternatively a top-level list:

[skills]
disabled_builtins = ["Skill Creator"]

This would let users curate exactly which skills are active, avoiding conflicts with custom skills that serve the same purpose.

Additional information

Related but distinct from #14161 (sub-agent [[skills.config]] overrides being ignored) — that issue is about per-agent overrides for custom skills. This request is about globally disabling built-in skills that ship with Codex itself.