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.

MEMORY.md

@@ -523,3 +523,11 @@ Scope: facts and traps that cost time to establish. Planned work lives in [TODO.
 - Precedent applied again: tag when the stated scope is done, carry blocked scope
   into the next patch rather than letting a release wait indefinitely on missing
   reference photography.
+
+## 2026-11-09 — Retail frontage and two pipeline traps
+
+- **`Tools/render_screenshots.sh` called `./Engine/...` for the capture step** while every commandlet above went through `run_cmdlet`'s `cd "$ENGINE"`. With `set -e` the script died at exit 127 *after* rebuilding the maps, so the PNGs silently stayed a day old and `--verify` never ran. Fixed to `"$ENGINE/Engine/Binaries/..."`. Symptom to remember: maps rebuild, screenshots do not move.
+- **The generic façade kit is applied to every actor labelled `Frontage_*` or `North_*`**, so staging a hand-modelled façade under those labels gets the kit pasted over it — two contradicting façade languages on one wall. `ue_apply_facade_kit.py` now skips `MODELLED` labels, and retail trim stages as `RetailTrim_*`.
+- **A Blender builder cannot be imported by a unit test** (`import bpy` at module scope). Pure layout arithmetic lives in `Tools/_common.py`; `Tools/tests/test_retail_frontage.py` tests it there, and the builder delegates. Same trick `fbx_export_preset.py` uses for its preset dicts.
+- **Joining 85 parts into one mesh per building** before export cut the Unreal import from 85 assets to 2, and the staging step to two spawns. Record per-part dimensions *before* the join: after it only the joined bounds exist.
+