test: cover scanner hidden-file defaults

[haosenwang1018]

Summary

• add coverage proving hidden files are still scanned when ignore_hidden=False
• keep the existing ignore_hidden=True test as the complementary branch
• cover the scanner's default hidden-file behavior with a focused unit test

Testing

• uv run ruff format tests/test_scanner.py
• uv run ruff check tests/test_scanner.py
• uv run python -m pytest tests/test_scanner.py -q

Closes #114