fix: TestSuiteGate should use project root cwd and current Python for pytest

[omsherikar]

Problem

TestSuiteGate.verify runs:

• subprocess.run(..., cwd=str(file_path.parent))
• Command python3 -m pytest (hard-coded interpreter)

So pytest often runs without the repo's pyproject.toml / pytest.ini / conftest.py context when the edited file is nested, and it may not use the same interpreter/venv as the host process.

Impact

False positives (tests fail for config reasons) or tests not discovered at all; CI vs local mismatch.

Suggested direction

• Use sys.executable instead of python3.
• Set cwd to the resolved project root (same as issue for threading project_root).
• Consider forwarding PYTHONPATH or documented env for edge cases.

References

• refactron/verification/checks/test_gate.py (subprocess.run, cwd)