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.

MEMORY.md

@@ -452,3 +452,25 @@ Scope: facts and traps that cost time to establish. Planned work lives in [TODO.
   storey spread is derived from the available height (`usable / storeys`) so the top
   band always lands inside the building. Result: 6922 9 × 11, theatre 8 × 6,
   6806 7 × 3, 6800 4 × 3, TCL 9 × 5.
+
+## 2026-11-09 — hero fluting + motto band; and a silent placement divergence
+
+- Fluting: 20 grooves per column as thin shadow-tone cylinders set into the shaft
+  (120 pieces) rather than boolean cuts — the eye reads them in silhouette and
+  grazing light, booleans would cost far more for that. Motto band is now a real
+  recess: surround 6 cm proud, panel 12 cm behind (was an 8 cm dark stripe).
+  Hero 148 parts/3 044 tris -> 271/5 492, still 14.50 m.
+- **The real find:** `ue_hero_facade_import.py` had its own hero position
+  `(-12024.5, -1450, 0)` — the pre-`0.1.0` value, before the frontage placement fix
+  moved the hero to `(-13336, +1307)`. Running the importer on its own therefore
+  teleported the hero **13 m east and onto the north side of the boulevard**, and
+  nothing complained: a displaced building still renders. The only symptom was the
+  reference score dropping 0.69 -> 0.56 with the 3x3 composition correlation
+  flipping +0.54 -> -0.08.
+- Fix: `Tools/ue_placement.py` is now the single source of truth (hero position,
+  verified frontage spans, `span_error`/`describe_span_failure`). Both
+  `ue_hero_facade_import.py` and `ue_build_demo_map.py` import it, the import asserts
+  the staged span and logs `PLACEMENT ERROR` when it does not match, and tests assert
+  the stale literal cannot come back. Spawn-view score back to **0.72** (best yet).
+- Lesson to keep: **duplicated placement constants drift silently.** The metric that
+  caught it was the composition correlation, not a visual review.