Add the photo-anchored variant pass with night and overcast facade frames

TODO.md

@@ -414,8 +414,11 @@ facade evidence is still the 2009 CC BY frame. The 8 downloaded candidates are i
       `scene_concepts._reference_source` requiring a refs-board `SIDECAR.md` row (or an explicit
       `--reference-unchecked`). Verified live on the El Capitan day concept anchored on the CC BY
       2.0 2009 facade photo; tests in `ReferenceGateTests`.
-- [ ] Add a sidecar-driven variant pass: for each real photo, generate day, night and weathered
-      variants of the same framing so the concept board stays comparable with the photo board.
+- [x] Add a sidecar-driven variant pass: `scene_concepts.py anchor --reference <photo>
+      --treatments day,night,weathered` generates same-framing variants with treatment clauses,
+      one `.refgen.json` provenance sidecar per frame. Verified live on the facade photo (night +
+      overcast frames committed; the weathered treatment reads as mild overcast — noted on the
+      board). Tests in `AnchorTests`.
 - [-] Generate facade, street and signage concept frames for the target block
       (`scene_concepts.py generate --reference ...`), commit only the selected frames, and record
       model, prompt, spend **and source photo** in the block sidecar. (First frame done: