Install metadata now records hook_runtime=codex-hookless-fallback and
references the hook runtime contract. Smoke test validates both fields.
Implements: ag-35a.3
- skills-codex/: 53 skills converted to Codex-native agents.md format
- install-codex-native-skills.sh: install to ~/.codex/agents/
- sync-codex-native-skills.sh: sync from source skills/ to skills-codex/
- test-codex-native-install.sh: integration tests for the install pipeline