Codex exec

Drive OpenAI's Codex CLI non-interactively via `codex exec` to delegate coding work to a second, independent agent. Use this skill when the user wants a second opinion on a design or bug, an independent implementation plan, an independent code review of a diff or PR, a self-contained implementation task run headlessly, parallel/background work on a sub-task, or cross-checking your own work against another model. Also use when the user explicitly mentions "codex", "codex exec", "codex review", or asks to "have codex plan / look at / build / review" something. Triggers: "ask codex", "get a second opinion from codex", "have codex plan this", "have codex review this", "run co…