materials: look-developed surface materials for every exported asset

Completes "Materials and look development for all exported assets". Every
exported surface previously carried a flat Constant3Vector fill, which read as
plastic. ensure_material() in Tools/ue_build_demo_map.py now builds a
procedural material per surface:

- base colour blended between two shades by world-space noise
  (WorldPosition -> Multiply -> Noise -> Lerp -> BaseColor) for large-scale
  variation,
- an explicit roughness and specular so the surface type is readable.

  M_Asphalt 0.92, M_Concrete 0.88, M_KerbConcrete 0.85, M_Ground 0.98,
  M_RoadPaint 0.62, M_FacadeStone 0.72, M_Stucco 0.86

Site meshes take their material by mesh name; the hero facade and the two
north-side buildings take theirs by actor label, so they are covered even
though other scripts stage them. Materials are deleted and rebuilt on every
run, so a look change cannot be masked by a stale asset.

Result: the facade reads as warm stone with surface variation, asphalt as dark
asphalt with grain, concrete and kerbs lighter and matte, and the north
buildings in stucco instead of flat grey.

Screenshots re-rendered and approved by the owner. The richer texture-based
pass (baked/procedural brick_facade, seamless_concrete, glass, material
instances) stays in the 0.1.4 facade patch.

Squash of branch materials-lookdev-0.1.0 (PR #5).

TODO.md

@@ -78,7 +78,7 @@ The MPFB character asset is planned as the NPC template (see `ROADMAP.md`). Keep
 - [x] Keep the character as a reusable NPC prefab: a visible body, a collision capsule, and a head-height check that the camera does not clip at 1.60 m — for when NPCs/pedestrians are wired in (`0.2.0+`), not the `0.1.0` player. Done 2026-11-07: `AGigLineNPCPerson` (C++), ACharacter with capsule half-height 83 cm / total 1.66 m (head at ~1.66 m, so a 1.60 m camera does not clip), the MPFB human on the built-in mesh as the visible body, `AutoPossessAI` for pedestrians; confirmed spawned feet-on-Z-0 and rendered in `Screenshots/review-npc-prefab` (☑ approved 2026-11-07).
 - [x] Screenshots use stable camera names (no index prefix), so inserting a shot no longer renumbers/ orphans files; `AGigLineShotActor` + `Screenshots/README.md` updated.
 
-### Asset production
+### Asset production - active - 01a1b26b-3c94-707f-9665-2f6b4a79b564 (branch `materials-lookdev-0.1.0`)
 
 - [x] Establish a consistent scale test, named export presets, and repeatable import settings. Scale test = the three-cube calibration scene (`Art/blender/scaletest/`, regenerable via `Tools/scale_test_export.py`); named export preset `ue_metric_v1` (FBX settings in that script); named import preset `ue_metric_v1` (`FbxImportUI` settings in `Tools/ue_scale_test_import.py`). Both scripts are the templates for production asset export/import.
 - [A] Collect reference photography for manual façade work. Local only, never committed: `Art/reference/` is gitignored. **72 images in eleven folders**: hero façades to 4k, the El Capitan Theatre exterior series, premiere-night staging, Ovation Hollywood, the north side, and the Lee Drug neighbour. Gaps largely closed by the Flickr/web-search pass: the hero entrance is now documented (three portals with individual short flights — the inherited "eight steps, 12 m wide" is overturned), and the 6806–6822 retail run appears in an oblique 2013 frame. Still missing: a clean isolated frame of the door recess and a night frame of 6840 itself.
@@ -87,7 +87,7 @@ The MPFB character asset is planned as the NPC template (see `ROADMAP.md`). Keep
 - [ ] Model surrounding block frontage.
 - [x] Model simplified background buildings directly across Hollywood Boulevard. Done 2026-11-07, the two in-scope north-side buildings — TCL Chinese Theatre (SM_TCL_Chinese_Theatre) and Madame Tussaud's (SM_Madame_Tussauds) — taken from the verified OSM blockout volumes and exported with `ue_metric_v1`, with a Y-mirror so they land north of Hollywood Blvd across the street from the hero (TCL spans Unreal Y 1802..9431, Tussaud's 1888..7586; road centreline ≈ 0, hero façade at Y −1450). Staged in the DemoMap as `North_TCL_Chinese` / `North_Madame_Tussauds`; demo shot `review-03-demo-north-buildings` captured. Simple flat facade materials (surfaces are the `0.1.4` patch).
 - [A] Build sidewalks, roads, and collision meshes. Terrain, road, sidewalks and kerbs exist (`Art/blender/terrain/`, `street/`) and are assembled in `site/site-2026-11-06.blend`; collision and details (crossing markings, kerb radii, aprons) are not built. Ground must follow the DEM: 3.94 m fall along the block, ~2 % crown between the gutters at ±10–11 m from the centreline, north sidewalk higher than south. Kerb height is an unresolved assumption — the DEM does not resolve it (`Geo/verification/2026-11-06-cross-sections.md`).
-- [ ] Materials and look development for all exported assets.
+- [x] Materials and look development for all exported assets. **Done 2026-11-07, screenshots approved.** every exported surface now carries a look-developed material built procedurally in `Tools/ue_build_demo_map.py` (`ensure_material`): base colour with a world-space noise blend between two shades for large-scale variation, plus an explicit roughness and specular. Set is `M_Asphalt` 0.92, `M_Concrete` 0.88, `M_KerbConcrete` 0.85, `M_Ground` 0.98, `M_RoadPaint` 0.62, `M_FacadeStone` 0.72 (hero façade) and `M_Stucco` 0.86 (TCL, Tussaud's), assigned by mesh and by actor label. Materials are rebuilt on every run so a stale asset cannot mask a look change. The richer texture-based pass (baked/procedural brick, brick_facade and seamless_concrete generators) stays in the `0.1.4` façade patch.
 
 ### Gameplay - active - 01a1b26b-3c94-707f-9665-2f6b4a79b564 (branch `gameplay-attribution-0.1.0`)