feat: duplicate detection via perceptual hashing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_analyzer.py

@@ -44,3 +44,26 @@ def test_normal_image_is_neither(tmp_path):
     path = make_test_image(tmp_path, color=(128, 128, 128))
     assert is_overexposed(path, threshold=240) is False
     assert is_underexposed(path, threshold=30) is False
+
+
+from analyzer import find_duplicates
+
+
+def test_identical_images_are_duplicates(tmp_path):
+    p1 = make_test_image(tmp_path, color=(100, 150, 200))
+    import shutil
+    p2 = tmp_path / "copy.jpg"
+    shutil.copy(p1, p2)
+    groups = find_duplicates([p1, str(p2)], threshold=0)
+    assert len(groups) == 1
+    assert len(groups[0]) == 2
+
+
+def test_different_images_are_not_duplicates(tmp_path):
+    from PIL import Image
+    p1 = make_test_image(tmp_path, color=(0, 0, 0))
+    img = Image.new("RGB", (100, 100), color=(255, 0, 0))
+    p2 = tmp_path / "red.jpg"
+    img.save(p2)
+    groups = find_duplicates([p1, str(p2)], threshold=0)
+    assert len(groups) == 0