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.

Tools/render_screenshots.sh

@@ -39,7 +39,10 @@ run_cmdlet ue_build_review_map.py "5/6 stage the demo shot cameras"
 tail -3 /tmp/ue-review-map-result.txt 2>/dev/null || true
 
 echo "== 6/6 capture the demo map =="
-./Engine/Binaries/Linux/UnrealEditor-Cmd "$PROJ" /Game/Hollywood/DemoMap \
+# The engine path is absolute: this step runs from the repo, not from $ENGINE, and a
+# bare ./Engine/... failed with "No such file or directory" while every commandlet
+# above succeeded through run_cmdlet's cd.
+"$ENGINE/Engine/Binaries/Linux/UnrealEditor-Cmd" "$PROJ" /Game/Hollywood/DemoMap \
   -game -windowed -ResX=1920 -ResY=1080 -nopause -nosplash -stdout
 
 echo "== collect the demo screenshots =="