feat(extract): Koordinaten, Kachel-Download und Mosaik

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tools/extract/tests/test_tiles.py

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+import numpy as np
+from leonida.tiles import assemble
+
+def fake_tile(row: int, col: int) -> np.ndarray:
+    # Jede Kachel einfarbig, Farbe kodiert Zeile und Spalte.
+    return np.full((256, 256, 3), (row, col, 7), dtype=np.uint8)
+
+def test_assemble_crops_to_slice():
+    mosaic = assemble(fake_tile)
+    assert mosaic.shape == (3000, 3000, 3)
+    # Nordwest-Ecke stammt aus Kachel (54, 60)
+    assert tuple(mosaic[0, 0]) == (54, 60, 7)
+    # Südost-Ecke stammt aus Kachel (65, 71)
+    assert tuple(mosaic[-1, -1]) == (65, 71, 7)