Add helper functions for Python plugin support in the supervisor:
- isPythonPlugin: detects Python plugins via .py extension or props.runtime
- findPythonInterpreter: discovers venv-first Python with PATH fallback
- sanitizePythonScriptPath: validates script paths preventing traversal
- buildPythonCommand: creates exec.Cmd with proper working dir and WaitDelay
- WithCommandFromManifest: unified option for Go and Python plugin commands
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>