Picture the duplicate originals review in the manual

The manual described the review (7c9a4ee) without a picture, because the
demo library holds no duplicates. The new duplicates scene makes two:
it copies two New York frames into a bck folder beside their own,
restarts the app so the scan finds them, waits for the sidebar row the
sweep's dating brings (54aee50), opens the review from it, presses
Check and takes the page. It deletes the copies and restarts on the
library as it was; record.sh's snapshot restore would remove them too.
It is registered last, so no other scene sees the copies.

The picture shows both groups proved the same file, the camera-named
copy outside bck marked Stays, and "Move 2 copies to trash" ready.

docs/manual/index.html

@@ -242,6 +242,7 @@ that stays will gain: the highest rating, every keyword and collection, a
 flag or label the copies agree on, faces and the names on them, and the
 edit if only a copy had one. Where the copies disagree on a flag or a
 label, the one that stays keeps its own and the line says so.</p>
+<figure><img loading="lazy" src="media/duplicates.png" alt="Two frames with a copy each in a bck folder, checked and proved the same, the copy that stays marked on each"><figcaption>Two frames with a copy each in a bck folder, checked and proved the same, the copy that stays marked on each</figcaption></figure>
 <p><code>Move N copies to trash</code> does it, one group at a time: each group is merged
 and its spare copies moved together, or not at all. The copies go to the
 trash, not away — select them in the trash view and <code>Restore</code> puts them