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).

MEMORY.md

@@ -185,3 +185,9 @@ Scope: facts and traps that cost time to establish. Planned work lives in [TODO.
 - **Camera placement in the demo map needs the mesh bounds, not intuition.** The hero façade body spans UE Y −1457..−200, so a "street level" camera at Y −400 is *inside* the building and renders its unlit back face. Read `get_bounding_box()` on the staged meshes before choosing a camera.
 - **"LIGHTING NEEDS TO BE REBUILT" (Build Lighting Only / `BuildLighting`) appears whenever a map has Stationary/Static lights and no baked lightmap.** For a fully dynamic scene the clean fix is `r.AllowStaticLighting=False` in `Config/DefaultEngine.ini` plus `set_mobility(ComponentMobility.MOVABLE)` on the directional light, sky light and height fog (and MOVABLE on the staged mesh components). Nothing to build, warning gone. Note the cvar is read at startup, so each new commandlet/game run picks it up.
 - The Android File Server `SecurityToken` kept reappearing in `Config/DefaultEngine.ini`; the plugin is disabled and excluded from shipping, so the value is cleared and must stay empty — it is a credential and must not be committed.
+
+## 2026-11-07 — Worktrees and the material look pass
+
+- **A fresh git worktree has no compiled game binaries.** `Binaries/` is gitignored, so `UnrealEditor-Cmd` on a new worktree exits "abnormally (error code: 1)" before running the Python script, with no Python error in the log. Run `Engine/Build/BatchFiles/Linux/Build.sh GigLineEditor Linux Development -project=<worktree>/Game/GigLine/GigLine.uproject` first.
+- `/tmp/gigline/*.txt` result files are **shared across worktrees**. Reading `/tmp/gigline/demo-map.txt` after a run can show another worktree's stale output — check the file mtime, or use a per-worktree result path.
+- **Flat Constant3Vector materials read as plastic.** Giving each surface a roughness plus a world-space-noise blend between two shades (WorldPosition → Multiply → Noise → Lerp between two Constant3Vectors → BaseColor) is enough to stop the blockout looking like a toy; no textures required.