lighting: fixed daytime rig, real surface materials, crossing fix

Fixed daytime lighting and basic ambience for the DemoMap:

- Sun pitch -50 / yaw 120 (intensity 4, warm), sky light 2.6 with real-time
  capture, sky atmosphere, height fog, and an unbound post-process volume with
  fixed exposure (min = max brightness) so no shot washes out or crushes to
  black depending on how much sky it frames.
- Root cause of the washed-out look was NOT the sun: Blender's flat diffuse
  colours do not survive the FBX->Unreal import. Every site material arrived
  white and the terrain arrived with WorldGridMaterial. The demo builder now
  creates and assigns M_Asphalt / M_Concrete / M_Ground / M_RoadPaint.
- Crossing fix: each zebra band was its own object, so Blender renamed the
  duplicates .001/.002 and site assembly (exact-name append) kept only one.
  All bands are now a single Crossing_Markings mesh (36 verts, 3 bands).
- Terrain gets a Ground_Earth material in the builder so it stops importing
  as a white grid.
- Demo cameras: street-level no longer sits inside the facade body (was
  rendering its back face), and the crossing camera aims at the designated
  s=130.1 crossing (UE X -14956) looking along the crosswalk.

Screenshots re-rendered; the four demo views are marked needs-review for the
owner's approval. MEMORY.md records the material-import, exposure,
light_color, band-naming and camera-bounds traps.

TODO.md

@@ -95,7 +95,7 @@ The MPFB character asset is planned as the NPC template (see `ROADMAP.md`). Keep
 - [~] Collision, reset, and pause functionality. Reset (**R**) and pause (**Escape**, a real game pause that releases the cursor) are implemented in `AGigLineCharacter` with `/Game/Input/IA_Reset` and `IA_Pause`. Collision now exists — terrain, road and sidewalks import as complex-as-simple, so a simple hull cannot ramp over the kerbs. **Not verified by hand**: walk, reset and pause need a human at the keyboard. No pause menu widget yet, only the pause itself.
 - [x] Build the walkable demo level: terrain, street, and hero facade assembled into one map with a start point on the north sidewalk, so the demo is something a player can walk rather than a review staging. **Built 2026-11-07** by `Tools/ue_build_demo_map.py` → `/Game/Hollywood/DemoMap`: sun/sky, `Hero_Facade`, six site meshes imported with collision (`Terrain_DEM`, `Road_Hollywood`, both sidewalks and both kerbs), and a `Demo_PlayerStart` on the north sidewalk 20 m back from the frontage. Demo views in `Screenshots/demo/` re-rendered and ☑ approved 2026-11-07.
 - [x] Walkable sidewalks and a designated street crossing. Crossing chosen: mid-block signalised crossing, OSM way 385648319, at 130 m along the block (`Geo/verification/2026-11-06-street-profile.md`). Done 2026-11-07: continental zebra markings (0.5 m bars / 0.5 m gaps, 3 m band) at all three signalised crossings, no collision on the paint; kerbs were already flushed at the crossings. Enablers found on the way: the street surfaces were 100 % down-facing (invisible in engine) — winding flipped; the terrain buried the street — 10.7 m corridor cut around the centreline (sidewalks cover the transition, walk-check 0 holes); LFS-lockable `.blend`/`.umap` check out read-only — builders now chmod before saving and fail loudly. Screenshot ☑ approved 2026-11-07 (`Screenshots/demo/review-demo-crossing`); the corridor renders near-black in shadow — that is the still-open **Fixed daytime lighting** item, not the crossing.
-- [-] Fixed daytime lighting and basic ambience. Current state: `Demo_Sun` at pitch −35, yaw 200 puts the street corridor in shadow — the crossing shot renders near-black. Plan: rotate sun yaw so light comes down the street axis (e/w), raise sun intensity, boost skylight fill, set fixed daytime (no time-of-day motion).
+- [-] Fixed daytime lighting and basic ambience. **Implemented 2026-11-07**, pending screenshot approval. Demo map now has a fixed daytime rig in `Tools/ue_build_demo_map.py`: sun pitch −50 / yaw 120 (intensity 4, warm 255/245/230, atmosphere sun light), sky light 2.6 with real-time capture, sky atmosphere, height fog (density 0.008), and a manual-exposure post-process volume (min = max brightness 1.0) so a shot cannot wash out or crush to black. Two root causes found while doing it: (a) **Blender flat diffuse colours do not survive the FBX→UE import** — every site mesh arrived white and the terrain arrived with `WorldGridMaterial`, which is what actually made the scene look blown out; explicit `M_Asphalt` / `M_Concrete` / `M_Ground` / `M_RoadPaint` materials are now created and assigned in the demo builder. (b) only **one of the three crossings** was reaching the game: each band was its own object and Blender renamed the duplicates `.001`/`.002`, which site assembly skips; all bands are now one `Crossing_Markings` object. Demo cameras also fixed: street-level sat inside the façade body, and the crossing camera aimed at the wrong crossing (s=36.6 instead of the designated s=130.1 at UE X −14956).
 - [ ] Geographic attribution display ("© OpenStreetMap contributors" + license link).
 
 ### Repository publication