feat(hero): sandstone, banners and recessed portals - the material was the missing link

Iterated the loop five times against Art/reference/hero-masonic/. What took the iterations was the material,
not the geometry:

- M_FacadeStone in /Game/Hollywood/Site is the KIT stone; the hero does not use it, so warming it changed
  nothing.
- The hero's materials come from the FBX and live at /Game/Hollywood/ElCapitan/M_Facade_*. Unreal keeps an
  existing material asset when an FBX referencing it is re-imported, so a Blender colour change never
  arrived.
- Deleting those materials before the import broke the mesh's slots: one colour, no banners, no windows.

The working step is tint_imported_materials(): import normally, then author one plain Constant3Vector
material per facade slot with the colour sampled from the reference, and assign it to the matching slot. The
elevation is now warm sandstone with ashlar coursing, three red banners, two window bands and three recessed
portals with steps.

Also: the portal's solid stone reveal z-fought with the door leaf and read as stripes, so the recess is
carried by jambs, lintel and shadow; banners are 1.35 x 6.2 m hung from 7.2 m instead of 1.55 x 5.4.

Loop iteration 5 verdict is still 'no': it wants the carved inscription, medallion relief, a crimson banner
tone and visible window grilles - all recorded as the next iteration. Rows 4-6 are pending review with the
new captures and two comparison plates.

Tools/ue_build_demo_map.py

@@ -472,10 +472,10 @@ def build():
         # Ashlar coursing at 0.55 m (a 0.10 m band joint), the reading the 2009
         # facade photograph gives for the hero's stone; roughness breaks up so the
         # wall is not one specular plane.
-        "M_FacadeStone": dict(dark=(0.62, 0.58, 0.50), bright=(0.76, 0.72, 0.64),
+        "M_FacadeStone": dict(dark=(0.30, 0.26, 0.20), bright=(0.47, 0.41, 0.31),
                               roughness=0.70, specular=0.32, noise_scale=0.005,
                               courses_m=0.55, joint_width=0.11,
-                              joint_tint=(0.40, 0.37, 0.32), roughness_variation=0.12,
+                              joint_tint=(0.16, 0.14, 0.11), roughness_variation=0.16,
                               texture="T_StoneAshlar", tile_cm=440.0),
         # Rendered/stucco frontage: no coursing, but a fine tooth and a wider
         # roughness range than before, because flat stucco is what read as plastic.
@@ -484,10 +484,10 @@ def build():
                          roughness_variation=0.20, texture="T_Stucco", tile_cm=260.0),
         # Stone in shadow: the hero's recessed wall behind the colonnade. Same
         # coursing as the face, a stop darker, so depth reads without a light.
-        "M_FacadeStoneShadow": dict(dark=(0.40, 0.37, 0.32), bright=(0.52, 0.49, 0.43),
+        "M_FacadeStoneShadow": dict(dark=(0.18, 0.155, 0.12), bright=(0.28, 0.24, 0.18),
                                     roughness=0.78, specular=0.26, noise_scale=0.005,
                                     courses_m=0.55, joint_width=0.11,
-                                    joint_tint=(0.28, 0.26, 0.23),
+                                    joint_tint=(0.10, 0.09, 0.07),
                                     roughness_variation=0.10),
         # Glazing: low roughness, strong specular. A plausible IOR for glass sits
         # near 1.5, which UE expresses through specular ~0.5-0.6 on an opaque