Changed ActionArgumentSchema.validate_name in src/cleveragents/action/schema.py:
- Replaced v.replace("-", "_").isidentifier() with v.isidentifier() so hyphens are correctly rejected instead of silently accepted
- Updated error message to say "Argument name must be a valid Python identifier (alphanumeric and underscores, not starting with a digit)" matching the BDD scenario assertion exactly
- Updated docstring to say "valid Python identifier"
ISSUES CLOSED: #3039