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/ue_build_demo_map.py

@@ -597,6 +597,25 @@ def build():
             staged_frontage += 1
     log(f"staged {staged_frontage} frontage buildings")
 
+    # --- retail frontage trim (0.1.6) -------------------------------------
+    # The two retail buildings beside the hero are modelled from their own
+    # photograph (Art/reference/retail-neighbours/); the trim is laid over the
+    # blockout volume, so it keeps the trim's own sampled materials rather than a
+    # look-dev override. 6822 Budget has no photograph and stays a bare volume.
+    for asset_name, label in (("SM_Retail_LeeDrug", "6800 Lee Drug trim"),
+                              ("SM_Retail_6806", "6806-6820 trim")):
+        mesh = unreal.EditorAssetLibrary.load_asset(f"/Game/Hollywood/Frontage/{asset_name}")
+        if mesh is None:
+            log(f"MISSING trim {asset_name} — run Tools/ue_import_retail_detail.py")
+            continue
+        # RetailTrim_ rather than Frontage_ so the kit assembler leaves it alone.
+        actor = spawn(unreal.StaticMeshActor, unreal.Vector(0, 0, 0), f"RetailTrim_{asset_name}")
+        if actor:
+            comp = actor.static_mesh_component
+            comp.set_static_mesh(mesh)
+            comp.set_mobility(unreal.ComponentMobility.MOVABLE)
+            log(f"staged: {label}")
+
     # --- player start: north sidewalk, facing the hero frontage -------------
     # Signs were measured from the imported meshes rather than assumed: the FBX
     # preset flips north, so in Unreal the road spans Y -1382..+1047, the NORTH