Replace Anthropic-specific _skill_args injection with standard CLI
argument conventions that work with any script regardless of origin.
Changes:
- Pass arguments via sys.argv (Python), process.argv (Node.js), and
positional parameters (Shell) instead of proprietary global injection
- Add arg_style parameter: "positional" (default), "named", or "env"
- positional: sys.argv = ['script.py', 'val1', 'val2']
- named: sys.argv = ['script.py', '--key1', 'val1', '--key2', 'val2']
- env: only SKILL_ARG_* environment variables
- Always set SKILL_ARG_* environment variables as fallback
- Fix CodeExecution missing 'log' attribute by calling before_execution()
- Update agent prompt documentation with new conventions and examples
This enables skills_tool to work with standard CLI scripts that use
sys.argv, argparse, click, or any other argument parsing method,
rather than requiring scripts to be written specifically for Agent Zero.
