lighting: fixed daytime rig, real surface materials, dynamic lights

Completes "Fixed daytime lighting and basic ambience" for 0.1.0. All 14
screenshots approved by the owner.

Lighting rig (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)
- Unbound post-process volume with fixed exposure (min == max brightness) so a
  shot cannot wash out or crush to black depending on how much sky it frames
- Dynamic-only: r.AllowStaticLighting=False plus MOVABLE lights and mesh
  components, so the editor's "LIGHTING NEEDS TO BE REBUILT" warning no longer
  fires and nothing needs baking

Bugs found and fixed on the way:
- Blender diffuse colours do not survive the FBX -> Unreal import: every site
  material arrived white and the terrain arrived with WorldGridMaterial, which
  is what actually made the scene look blown out. The demo builder now creates
  and assigns M_Asphalt, M_Concrete, M_Ground and M_RoadPaint.
- Only one of the three crossings reached the game: each zebra band was its own
  object, so Blender renamed the duplicates .001/.002 and exact-name site
  assembly skipped them. All bands are now one Crossing_Markings mesh.
- Demo cameras: street-level sat inside the facade body (rendering its unlit
  back face) and the crossing camera aimed at the s=36.6 crossing instead of
  the designated s=130.1 (UE X -14956).
- The terrain had no material and imported as a bright default grid.
- Cleared a committed Android File Server SecurityToken (plugin disabled and
  shipping-excluded; the value must stay empty).

Docs:
- Screenshots/README.md: one consolidated table for all 14 shots with map,
  camera view and description; all approved.
- MEMORY.md: records the material-import, exposure, light_color struct,
  band-naming, camera-bounds and lighting-build traps.
- TODO.md: lighting item marked done.

Squash of branch gameplay-lighting-0.1.0 (PR #3).

Game/GigLine/Config/DefaultEngine.ini

@@ -2,7 +2,12 @@
 GlobalDefaultGameMode="/Script/GigLine.GigLineGameModeBase"
 
 [/Script/Engine.RendererSettings]
-; Leave defaults for 0.1.0; quality preset is documented at release time.
+; Dynamic-only lighting. With static lighting allowed, the stationary sun and
+; sky light demanded a baked lighting build and the editor warned
+; "LIGHTING NEEDS TO BE REBUILT" (Build Lighting Only / BuildLighting) on every
+; map. The demo is a fixed daytime scene lit entirely dynamically, so disable
+; static lighting outright — nothing to build, no warning.
+r.AllowStaticLighting=False
 
 [URL]
 GameName=GigLine
@@ -10,7 +15,9 @@ GameName=GigLine
 [/Script/AndroidFileServerEditor.AndroidFileServerRuntimeSettings]
 bEnablePlugin=False
 bAllowNetworkConnection=False
-SecurityToken=01A1B5CDAFDE7AAEB5DFBB48880D25DE
+; SecurityToken intentionally empty: it is a credential, and the plugin is
+; disabled and excluded from shipping. Never commit a real token here.
+SecurityToken=
 bIncludeInShipping=False
 bAllowExternalStartInShipping=False
 bCompileAFSProject=False