feat(facades): 0.1.6 retail frontage first pass — Lee Drug and 6806-6820

Models the two retail buildings beside the hero from their own photograph rather
than the generic kit: bronze cornice, mural row, lettering band, stepped Deco
parapet and rounded corner tower on 6800 Lee Drug; burgundy fascia, pilasters,
white-framed windows and banded parapet on 6806-6820. Reference analysis written
before any geometry (Art/blender/retail/ref-analysis.md), every unmeasured
proportion carried into the part report as an assumption.

6822 Budget is deferred, not guessed: no photograph of it exists and the 6.0 x 5.5 m
sliver cannot be read out of the neighbour shot.

Pipeline fixes found on the way:
- render_screenshots.sh called ./Engine/... for the capture step while every
  commandlet used the absolute path; set -e killed the script at 127 *after* the
  maps were rebuilt, so screenshots silently stayed a day old.
- the facade kit applies to every Frontage_*/North_* actor, so it pasted its own
  language over the new modelled facades; it now skips them, and the trim stages as
  RetailTrim_*.
- pure bay arithmetic moved to Tools/_common.py so it is unit-testable without
  Blender (4 new tests, 82 total pass).

Known gaps recorded in Screenshots/README.md, not hidden: the parapet reads as a
blank band, murals and lettering do not resolve at review distance, the tower is a
plain cylinder, and the review camera crops the east end.

TODO.md

@@ -15,7 +15,10 @@ Suggested blender skills: **references** (reference-image-match), **archviz**, *
 
 ### Patch tasks - active - session-5598ce7e-27e3-4c64-bb49-c04a4a31ee58 (branch `facade-retail-0.1.6`)
 
-- [A] **Model 6822 Budget, 6806–6820 and 6800 Lee Drug from their own references.** `Art/reference/retail-neighbours/` holds 6800 and its neighbour (Gb321, CC BY-SA 4.0); Commons has nothing usable for 6822 or 6806–6820, so those two need photography before they can be modelled honestly. Do not substitute the El Capitan Theatre's 18-frame set — it would misattribute the façades.
+- [A] **Model 6800 Lee Drug and 6806–6820 from their own reference.** First pass 2026-11-09 on branch `facade-retail-0.1.6`: `Tools/retail_frontage_build.py` builds both façades from the one photograph (`Art/reference/retail-neighbours/`, Gb321 CC BY-SA 4.0) with the analysis in `Art/blender/retail/ref-analysis.md`;
+  `Tools/ue_import_retail_detail.py` imports them and the demo builder stages them as `RetailTrim_*`. The generic façade kit is now skipped on these two, so their walls carry one façade language instead of two.
+  **Open on this item:** the parapet reads as a blank band, the mural row and lettering band do not resolve at review distance, the corner tower is a plain cylinder, and the review camera crops the east end — all listed in `Screenshots/README.md`.
+- [D] **Model 6822 Budget.** Deferred: no photograph exists for it (Commons has nothing usable) and the single-storey 6.0 × 5.5 m volume cannot be read from the neighbour shot. Needs photography before it can be modelled honestly; do not substitute the El Capitan Theatre's set or the 6806–6820 shot.
 - [ ] Review every façade change with `Tools/render_screenshots.sh --verify` before tagging.
 - [ ] Tag `v0.1.6` and write `CHANGELOG.md` entry; then remove this section.