Apply review feedback: use standard comments and tmp_path fixture

[Copilot]

Address code review feedback from PR #482 on visualization auto-scaling changes.

Changes

• defaults.py: Replace triple-quoted strings with standard # comments to avoid creating module-level string constants at import time
• test_auto_scale.py: Migrate from deprecated tmpdir to tmp_path fixture for pathlib-native testing, remove unused fixture parameters

# Before
def test_auto_scale_save(self, large_image, detection_result_large, tmpdir):
    path = Path(tmpdir) / "test_auto_scale.jpg"

# After  
def test_auto_scale_save(self, large_image, detection_result_large, tmp_path):
    path = tmp_path / "test_auto_scale.jpg"

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