feat(hero): fluting and a recessed motto band; placement gets one source of truth

Hero detail:
- Fluting: 20 grooves per column as thin shadow-tone cylinders set into the shaft
  (120 pieces) rather than boolean cuts - readable in silhouette and grazing light
  at a fraction of the cost.
- Motto band: real recess with a moulded surround 6 cm proud and the panel 12 cm
  behind, replacing the 8 cm dark stripe.
  Hero 148 parts/3044 tris -> 271/5492, still 14.50 m.

Placement bug this exposed (a real one, invisible in a render):
- ue_hero_facade_import.py carried its own hero position (-12024.5, -1450) from
  before the 0.1.0 frontage fix, so running the importer alone moved the hero 13 m
  east and onto the north side of the boulevard. Only symptom: the reference score
  fell 0.69 -> 0.56 and the 3x3 composition correlation flipped +0.54 -> -0.08.
- New Tools/ue_placement.py is the single source of truth (hero position, verified
  frontage spans, span validators). Both the importer and the demo builder use it;
  the import asserts the staged span and logs PLACEMENT ERROR otherwise.
- 11 new tests, including one that fails if the stale literal returns. 78 total.

Spawn-view score recovered to 0.72 (best yet); screenshots verified 4/4, packaged QA
all PASS.

Art/blender/hero/hero-facade-2026-11-07.json

@@ -37,6 +37,15 @@
       ],
       "evidence": "6 columns at 4.96 m centres (sibling notes x measured frontage)"
     },
+    {
+      "object": "Hero_Flute_x120",
+      "dims_m": [
+        0.064,
+        0.064,
+        6.53
+      ],
+      "evidence": "photographs: fluted shafts; 20 grooves per column modelled as shallow cylinders in the shadow tone rather than boolean cut grooves"
+    },
     {
       "object": "Hero_ColumnBase_x6",
       "dims_m": [
@@ -104,10 +113,10 @@
       "object": "Hero_MottoBand",
       "dims_m": [
         22.75,
-        0.08,
+        0.1,
         0.85
       ],
-      "evidence": "photographs: motto panel above the colonnade"
+      "evidence": "photographs: motto panel above the colonnade, now an inset panel with a moulded surround rather than a flat stripe"
     },
     {
       "object": "Hero_Medallion_x2",