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/tests/test_ue_placement.py

@@ -0,0 +1,86 @@
+"""Tests for Tools/ue_placement.py — the single source of truth for placement.
+
+A regression test for a real bug: `ue_hero_facade_import.py` carried its own hero
+position (the pre-0.1.0 one) while `ue_build_demo_map.py` staged the verified one.
+Running the importer moved the hero 13 m east and onto the north side of the
+boulevard, and nothing complained because a displaced building still renders.
+"""
+
+import os
+import sys
+import unittest
+
+ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", ".."))
+sys.path.insert(0, os.path.join(ROOT, "Tools"))
+
+import ue_placement  # noqa: E402
+
+
+class HeroPlacementTest(unittest.TestCase):
+    def test_hero_actor_name(self):
+        self.assertEqual(ue_placement.HERO_ACTOR, "Hero_Facade")
+
+    def test_hero_location_is_the_verified_building_line(self):
+        x, y, z = ue_placement.HERO_LOCATION_CM
+        self.assertEqual((x, y, z), (-13336.0, 1307.0, 0.0))
+        # North is -Y in Unreal, so the hero on the south side must have Y > 0.
+        self.assertGreater(y, 0.0, "hero must be on the south side (Y > 0)")
+
+    def test_hero_span_is_verified(self):
+        # The mesh spans -1308..+1308 cm in X about its origin.
+        lo = ue_placement.HERO_LOCATION_CM[0] - 1308.0
+        hi = ue_placement.HERO_LOCATION_CM[0] + 1308.0
+        exp_min, exp_max, ok = ue_placement.span_error("hero", lo, hi)
+        self.assertTrue(ok)
+        # The mesh spans exactly the verified footprint, so the two agree.
+        self.assertAlmostEqual(exp_min, lo, delta=ue_placement.SPAN_TOLERANCE_CM)
+        self.assertAlmostEqual(exp_max, hi, delta=ue_placement.SPAN_TOLERANCE_CM)
+
+
+class SpanValidatorTest(unittest.TestCase):
+    def test_misplaced_hero_is_reported(self):
+        # The exact failure observed: the stale import position put the hero here.
+        lo, hi = -13332.0, -10716.0
+        exp_min, exp_max, ok = ue_placement.span_error("hero", lo, hi)
+        self.assertFalse(ok)
+        message = ue_placement.describe_span_failure("hero", lo, hi)
+        self.assertIn("does not match the verified", message)
+        self.assertIn(f"{exp_min:.0f}", message)
+
+    def test_correct_span_reports_nothing(self):
+        self.assertEqual(ue_placement.describe_span_failure("hero", -14644, -12028), "")
+
+    def test_within_tolerance_passes(self):
+        # 99 cm off is inside the ±100 cm tolerance.
+        self.assertTrue(ue_placement.span_error("6922", -24276 + 99, -17700 - 99)[2])
+
+    def test_outside_tolerance_fails(self):
+        self.assertFalse(ue_placement.span_error("6922", -24276 + 101, -17700)[2])
+
+    def test_unknown_building_raises(self):
+        with self.assertRaises(KeyError):
+            ue_placement.span_error("no-such-building", 0, 0)
+
+    def test_every_frontage_span_is_ordered(self):
+        for name, (lo, hi) in ue_placement.FRONTAGE_SPANS_CM.items():
+            self.assertLess(lo, hi, f"{name} span is inverted")
+
+
+class SingleSourceOfTruthTest(unittest.TestCase):
+    """The import script and the demo builder must not carry their own literals."""
+
+    def test_import_script_uses_the_shared_constant(self):
+        src = open(os.path.join(ROOT, "Tools", "ue_hero_facade_import.py"),
+                   encoding="utf-8").read()
+        self.assertIn("ue_placement.HERO_LOCATION_CM", src)
+        self.assertNotIn("(-12024.5, -1450.0, 0.0)", src,
+                         "the stale pre-0.1.0 hero position must not come back")
+
+    def test_demo_builder_uses_the_shared_constant(self):
+        src = open(os.path.join(ROOT, "Tools", "ue_build_demo_map.py"),
+                   encoding="utf-8").read()
+        self.assertIn("ue_placement.HERO_LOCATION_CM", src)
+
+
+if __name__ == "__main__":
+    unittest.main()