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.

Tools/ue_hero_facade_import.py

@@ -19,14 +19,19 @@ import unreal
 
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 import ue_common  # noqa: E402
+import ue_placement  # noqa: E402
 
 FBX = "/tmp/gigline/hero-facade.fbx"
 DEST = "/Game/Hollywood/ElCapitan"
-ACTOR_LABEL = "Hero_Facade"
+ACTOR_LABEL = ue_placement.HERO_ACTOR
 LEVEL = "/Game/Hollywood/DemoMap"
 
 # Unreal centimetres: south-east corner of the façade, on the building line.
-PLACEMENT_CM = (-12024.5, -1450.0, 0.0)
+# Placement lives in Tools/ue_placement.py. It used to be a literal here, and it
+# drifted from ue_build_demo_map.py: this file kept the pre-0.1.0 position
+# (-12024.5, -1450) while the builder staged (-13336, 1307), so running the importer
+# on its own moved the hero 13 m east and onto the north side of the boulevard.
+PLACEMENT_CM = ue_placement.HERO_LOCATION_CM
 
 RESULT = "/tmp/gigline/hero-facade-import.txt"
 lines = []
@@ -118,6 +123,17 @@ def measure_and_place():
     comp.set_static_mesh(asset)
     comp.set_mobility(unreal.ComponentMobility.STATIC)
     log(f"placed {ACTOR_LABEL} at {PLACEMENT_CM} (cm) on {LEVEL}")
+
+    # Prove it landed on its verified footprint, not merely that it spawned.
+    box = asset.get_bounding_box() if asset else None
+    if box:
+        lo = box.min.x + PLACEMENT_CM[0]
+        hi = box.max.x + PLACEMENT_CM[0]
+        problem = ue_placement.describe_span_failure("hero", lo, hi)
+        if problem:
+            log(f"PLACEMENT ERROR: {problem}")
+        else:
+            log(f"span ok: X {lo:.0f}..{hi:.0f}")
     _make_map_writable(LEVEL)
     saved = unreal.EditorLoadingAndSavingUtils.save_map(
         unreal.EditorLevelLibrary.get_editor_world(), LEVEL)