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.

Tools/hero_facade_build.py

@@ -147,6 +147,14 @@ def build():
     # Inset so the entablature (1.5 m deep) and parapet (1.2 m deep) sit inside the
     # measured 25.75 m frontage instead of overhanging it.
     inset = 0.75
+    # The wall's front face, and the only Y that matters for what is visible.
+    # +Y is the street side: anything with y < FRONT_Y is inside the solid mass and never renders.
+    # Hand-typed negative Y values throughout this file put the banners 55 cm, the portals 2 m and
+    # the windows 6 cm behind this plane, which is why the captures showed a plain block with six
+    # columns. `seat_on_front()` below re-seats every applied detail relative to FRONT_Y, so the
+    # depth is stated once instead of guessed at each call site.
+    global FRONT_Y
+    FRONT_Y = -BODY_D / 2.0 - 0.5 + BODY_D / 2.0  # = -0.5 with the current BODY_D
     cube("Hero_Mass", 0.0, -BODY_D / 2.0 - 0.5, HEIGHT / 2.0, FRONTAGE_W - 2 * inset, BODY_D, HEIGHT, stone_dark)
     note("Hero_Mass", (FRONTAGE_W - 2 * inset, BODY_D, HEIGHT),
          "measured frontage x assumption depth x measured height, inset behind the cornice")
@@ -350,9 +358,47 @@ def build():
             cube(f"Hero_Window_{rank}_{i}", wx, WINDOW_Y, z, 2.0, 0.08, 1.9, glass)
     note("Hero_Window_x10", (2.0, 0.08, 1.9), "photographs: window bands behind the colonnade")
 
+    # --- seat the applied detail on the wall ---------------------------------
+    # Depth is a property of the façade, not of each call site: state it once here. Parts whose
+    # front face is behind the wall plane are moved until it sits at FRONT_Y + offset.
+    seat_on_front((
+        ("Hero_Architrave", 0.05), ("Hero_Cornice", 0.05), ("Hero_Dentil", 0.05),
+        ("Hero_Entablature", 0.03), ("Hero_MottoBand", 0.06), ("Hero_MottoSurround", 0.06),
+        ("Hero_Medallion", 0.08), ("Hero_Banner", 0.08), ("Hero_Window", 0.03),
+        ("Hero_Portal", 0.05), ("Hero_PortalJamb", 0.08), ("Hero_PortalLintel", 0.08),
+        ("Hero_PortalMullion", 0.04), ("Hero_PortalSign", 0.10),
+    ))
+
     return parts, lines
 
 
+def seat_on_front(table):
+    """Move each named part so its street-facing face sits `offset` metres proud of FRONT_Y.
+
+    `table` is (name_prefix, offset_m) pairs. Parts that name no prefix - the mass, the colonnade,
+    the steps and the stylobate - are left where the geometry put them, because they define the
+    plane rather than hang on it.
+    """
+    moved = 0
+    for obj in bpy.data.objects:
+        if obj.type != "MESH":
+            continue
+        for prefix, offset in table:
+            if not obj.name.startswith(prefix):
+                continue
+            world_ys = [(obj.matrix_world @ v.co).y for v in obj.data.vertices]
+            front = max(world_ys)
+            delta = (FRONT_Y + offset) - front
+            if abs(delta) < 1e-4:
+                moved += 1
+            else:
+                obj.location.y += delta
+            print(f"[hero] seat {obj.name:22} y {front:+.2f} -> {front + delta:+.2f} (offset {offset:+.2f})")
+            moved += 1
+            break
+    print(f"[hero] seated {moved} parts on the wall plane at Y {FRONT_Y:+.2f}")
+
+
 def export_fbx(path):
     # Preset lives in Tools/fbx_export_preset.py (ue_metric_v1).
     os.makedirs(os.path.dirname(path), exist_ok=True)