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/README.md

@@ -22,6 +22,7 @@ Geographic tools live in [`Geo/tools/`](../Geo/README.md) and the Blender-side b
 | `ue_stage_theatre_trim.py` | Imports the trim to `/Game/Hollywood/Theatre` and stages one actor per piece in the DemoMap with site materials; clears a previous run first. |
 | `ue_apply_facade_kit.py` | Lays the kit over a building's street face from its own bounding box: bay count = round(width / 4.96), storeys from the height, shopfronts on the ground floor, windows above, pilasters on bay boundaries, cornice and parapet at the top. Clears a previous application first; unique labels per building. |
 | `generate_facade_textures.py` | Deterministic stdlib PNG generator for the facade maps (`T_StoneAshlar`, `T_Stucco`, `T_Asphalt`, `T_Concrete`, each `_BC` base colour + `_R` roughness). Pure-zlib writer, hash-based value noise, identical bytes on every run; `--size` and `--out` (`/tmp/gigline/textures` by default). `ue_build_demo_map.py` imports them into `/Game/Hollywood/Textures` and samples them world-aligned. |
+| `ue_placement.py` | Single source of truth for where staged actors belong in the DemoMap (hero position, verified frontage spans) plus `span_error`/`describe_span_failure` validators. Exists because the hero position was written twice and drifted — the importer kept the pre-`0.1.0` value and moved the hero 13 m east onto the wrong side of the boulevard. No `unreal` import, so it is unit-tested. |
 | `ue_common.py` | Shared helpers for the Unreal commandlet scripts: `make_writable()` clears the read-only bit an LFS `.umap` checks out with (otherwise `save_map()` returns False silently), and `require_saved()` makes that failure explicit. |
 | `fbx_export_preset.py` | The **single** FBX export preset (`ue_metric_v1` / `ue_character_v1`): metres→centimetres via `FBX_SCALE_NONE`, axis mapping east +X / north −Y / up +Z, `mesh_smooth_type="FACE"` (smoothing groups survive the import). Every Blender exporter imports it instead of copying the argument block; `preset_kwargs()` is bpy-free and unit-tested. |
 | `sibling_asset_audit.py` | Reads the sibling project's prop library from GLB headers into `Art/props/reuse-manifest.json`; copies nothing |