fix(hero): seat the façade detail on the wall, so it renders at all

The three hero captures showed a plain block with six columns because every applied detail sat BEHIND the
wall's front face, inside the solid mass:

  Hero_Banner_1   y -1.08..-1.02   (55 cm inside)
  Hero_Portal_1   y -2.35..-1.15   (2 m inside)
  Hero_Window_1_1 y -0.60..-0.52   (2 cm inside)

The colonnade, cornice and dentils happened to protrude, which is exactly what the shots showed.

The depth is now stated once, in hero_facade_build.py: FRONT_Y is the wall's front face and
seat_on_front() moves every applied part until its street-facing face sits at FRONT_Y + offset - 8 cm for
banners and jambs, 5 cm for entablature and cornice, 3 cm for window panes, 4 cm for mullions, 10 cm for
portal signs. It reports what it moved, 99 parts.

After re-export, re-import and re-render the front elevation now shows the three red banners, the two
window bands, the dentil course and the portals. What is still missing against the reference: rusticated
banding on the stone, lettering on the motto band, grilles in the windows, a balustrade on the parapet, and
the blank lintel band across the portals that the reference does not have.

Rows 4, 5 and 6 are back to pending for review because the images changed.

Screenshots/README.md

@@ -16,9 +16,9 @@ Both capture passes are produced by [`Tools/render_screenshots.sh`](../Tools/ren
 | 1 | ReviewMap | ![character feet](review/review-character-feet.png) | [x] | approved |
 | 2 | ReviewMap | ![character](review/review-character.png) | [x] | approved |
 | 3 | ReviewMap | ![ground contact](review/review-ground-contact.png) | [x] | approved |
-| 4 | ReviewMap | ![hero facade front](review/review-hero-facade-front.png) | [ ] | moved to its own task: TODO.md -> hero facade rework |
-| 5 | ReviewMap | ![hero facade oblique](review/review-hero-facade-oblique.png) | [ ] | moved to its own task: TODO.md -> hero facade rework |
-| 6 | ReviewMap | ![hero portals](review/review-hero-portals.png) | [ ] | moved to its own task: TODO.md -> hero facade rework |
+| 4 | ReviewMap | ![hero facade front](review/review-hero-facade-front.png) | [ ] | re-rendered after the detail was seated on the wall: banners, windows, portals and dentils are visible now; still flat stone, no lettering, blank band over the portals |
+| 5 | ReviewMap | ![hero facade oblique](review/review-hero-facade-oblique.png) | [ ] | re-rendered after the detail was seated on the wall: banners, windows, portals and dentils are visible now; still flat stone, no lettering, blank band over the portals |
+| 6 | ReviewMap | ![hero portals](review/review-hero-portals.png) | [ ] | re-rendered after the detail was seated on the wall: banners, windows, portals and dentils are visible now; still flat stone, no lettering, blank band over the portals |
 | 7 | ReviewMap | ![npc prefab](review/review-npc-prefab.png) | [x] |  |
 | 8 | ReviewMap | ![overview](review/review-overview.png) | [x] | approved |
 | 9 | ReviewMap | ![player placement](review/review-player-placement.png) | [x] | approved |