Fix Space metadata and publish core test

tests/test_core.py

@@ -0,0 +1,15 @@
+import numpy as np
+
+from core import image_billboard_points, write_preview_ply
+
+
+def test_billboard_preview_is_finite_and_colored(tmp_path):
+    image = np.zeros((4, 6, 3), dtype=np.uint8)
+    image[..., 0] = 200
+    points, colors = image_billboard_points(image, max_side=6)
+    assert points.shape == (24, 3)
+    assert colors.shape == (24, 3)
+    assert np.isfinite(points).all()
+    assert np.all(colors[:, 0] == 200)
+    path = write_preview_ply(tmp_path / "preview.ply", points, colors)
+    assert "element vertex 24" in path.read_text(encoding="utf-8")