📝 **Task:** Implement `SkillRegistry`: * `register(name: str, system: str) -> int` — adds a new version, returns its 1-based version number. * `resolve(spec: str) -> str` — `spec` is either `'name'` (return the LATEST system prompt) or `'name@N'` (return version N exactly). Raise `KeyError` if the name or version doesn't exist. The driver exercises four scenarios: canonical pin/latest, out-of-range version, unknown skill, non-numeric version, then re-isolation across two skills. Expected output: ``` 1 2 v2: be helpful and brief v1: be helpful missing missing missing 1 route urgent issues v2: be helpful and brief ``` 📋 Implement the function above. Tests run automatically. 💡 **Hint:** Re-read the theory if stuck.