fix(#683): claw skills remove/add/uninstall/delete emits typed error, exit 1

- Add unsupported skills action guard in parse_args for remove/add/uninstall/delete
- Add unsupported_skills_action to classify_error_kind for structured JSON errors
- Fix pre-existing compile errors (stale retry_after field, missing Team variant)
- Add regression test unsupported_skills_actions_return_typed_error_683

Author: code-yeongyu