Add scoped Codex configuration target

[DROOdotFOO]

Summary

• add Codex AGENTS guidance, lifecycle hooks, and MCP registration
• merge upstream and vendored skills into one shared Codex, Claude Code, and Raxol inventory
• add a scoped Codex apply workflow that binds this checkout and excludes unrelated home files
• preserve SSH commit signing and Foundry, Grok, Aztec, and Nargo PATH state
• add migration, hook, MCP, configuration-preservation, and target-allowlist tests

Verification

• make codex-check
• make lint
• chezmoi verify
• scoped make codex-diff contains only .agents and .codex
• zero rendered diff for .gitconfig, .zshenv, and .zshrc
• live scoped apply: 60 merged skills and 13 enabled MCP servers
• git diff --check