Workflow JSON params can now reference environment variables (e.g.
${env:QUAKE3_PAK0}) which are expanded at JSON load time. A new Python
detector reads the Windows registry and parses libraryfolders.vdf to
locate Steam libraries, then resolves known-game files into env vars
that dev_commands.py exports before launching the engine. Lets users
with legitimate Steam-owned game data run packages like quake3 without
hardcoded paths.
Also fixes os.execv on Windows (Invalid argument with spaced paths) by
falling back to subprocess.call.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
