derive cleaner min-4px YOLO corpus

tests/test_derive_yolo_min_dimension_corpus.py

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+import pytest
+
+from scripts.derive_yolo_min_dimension_corpus import filter_label_lines
+
+
+def test_filter_label_lines_removes_only_rows_below_pixel_floor() -> None:
+    lines = [
+        "0 0.5 0.5 0.005 0.25",
+        "0 0.5 0.5 0.0078125 0.25",
+        "0 0.5 0.5 0.1 0.1",
+    ]
+
+    kept, removed = filter_label_lines(lines, tile_size=512, min_dimension_pixels=4)
+
+    assert kept == lines[1:]
+    assert removed == [0]
+
+
+def test_filter_label_lines_rejects_invalid_source_rows() -> None:
+    with pytest.raises(ValueError, match="invalid YOLO row"):
+        filter_label_lines(["0 0.5 0.5"], tile_size=512, min_dimension_pixels=4)