fix(skill): recover Windows interpreter without parsing launcher

[oleksii-tumanov]

Summary

• Recover a missing .graphify_python from validated uv and pipx tool environments before considering console-script shebang and system-Python fallbacks.
• Require both an installed graphifyy distribution and an importable graphify module, rejecting project-local shadow modules and broken metadata-only environments.
• Regenerate the skill artifacts and cover both tool managers, an MZ-prefixed Windows launcher, and the existing POSIX shebang path.

Addresses A1 in #1619.

Result

Path-sanitized results from the Windows regression harness:

uv -> <tmp>/uv-tools/graphifyy/Scripts/python.exe
pipx -> <tmp>/pipx-tools/graphifyy/Scripts/python.exe
cwd shadow module -> rejected
metadata without module -> rejected

Testing

• python -m pytest tests/test_skillgen.py -q (64 passed)
• python -m pytest tests/ -q --tb=short (3398 passed, 4 skipped)
• python -m tools.skillgen --check, --audit-coverage, --schema-singleton, --monolith-roundtrip, and --always-on-roundtrip (passed; 134 generated artifacts match)
• python -m ruff check tests/test_skillgen.py (passed)