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).

Tools/ue_build_review_map.py

@@ -96,11 +96,28 @@ try:
         else:
             log("floor spawn failed")
 
-    if spawn(unreal.DirectionalLight, unreal.Vector(0, 0, 900), "RenderKeyLight",
-             rot=unreal.Rotator(pitch=-38.0, yaw=35.0, roll=0.0)):
-        log("staged: DirectionalLight")
-    if spawn(unreal.SkyLight, unreal.Vector(0, 0, 1200), "RenderFillSky"):
-        log("staged: SkyLight")
+    # Lights are Movable and the project disables static lighting
+    # (r.AllowStaticLighting=False), so no baked lighting build is needed and
+    # the editor stops asking to rebuild lighting.
+    sun = spawn(unreal.DirectionalLight, unreal.Vector(0, 0, 900), "RenderKeyLight",
+                rot=unreal.Rotator(pitch=-38.0, yaw=35.0, roll=0.0))
+    if sun:
+        comp = sun.get_component_by_class(unreal.DirectionalLightComponent)
+        if comp:
+            try:
+                comp.set_mobility(unreal.ComponentMobility.MOVABLE)
+            except Exception as exc:  # noqa: BLE001
+                log(f"key light mobility not set: {exc!r}")
+        log("staged: DirectionalLight (movable)")
+    sky = spawn(unreal.SkyLight, unreal.Vector(0, 0, 1200), "RenderFillSky")
+    if sky:
+        comp = sky.get_component_by_class(unreal.SkyLightComponent)
+        if comp:
+            try:
+                comp.set_mobility(unreal.ComponentMobility.MOVABLE)
+            except Exception as exc:  # noqa: BLE001
+                log(f"fill sky mobility not set: {exc!r}")
+        log("staged: SkyLight (movable)")
     if spawn(unreal.SkyAtmosphere, unreal.Vector(0, 0, 0), "RenderSky"):
         log("staged: SkyAtmosphere")
 
@@ -258,8 +275,17 @@ try:
             # 14 m back so the 14.5 m elevation fits: at 2 m the camera sees only
             # the colonnade's underside.
             ("demo-spawn-view", unreal.Vector(-10722.5, -3500, 165), unreal.Vector(-10722.5, -1450, 700)),
-            ("demo-street-level", unreal.Vector(-11000, -400, 165), unreal.Vector(-10722.5, -1450, 500)),
-            ("demo-crossing", unreal.Vector(-23750, -1800, 480), unreal.Vector(-24291, -1400, 300)),
+            # Street level, from the north sidewalk: the old camera sat at Y -400,
+            # inside the facade body (which spans Y -1457..-200), so it looked at
+            # the unlit back face. Y -2600 is on the sidewalk in front of the lit
+            # elevation.
+            ("demo-street-level", unreal.Vector(-10850, -2600, 170), unreal.Vector(-10722.5, -1450, 400)),
+            # The designated mid-block crossing. Street arc length runs from the
+            # west end (s=0 at X -27966 cm), so s=130.1 m is UE X -14956, not the
+            # -24291 the old camera used (that is the s=36.6 crossing). Camera sits
+            # on the north sidewalk looking along the crosswalk itself, which is
+            # the pedestrian's view and shows the zebra bars as bars.
+            ("demo-crossing", unreal.Vector(-15250, -2500, 400), unreal.Vector(-14956, 400, 150)),
             # the two north-side background buildings (TCL, Tussaud's) seen from
             # the south sidewalk, across Hollywood Blvd: their frontage and mass.
             ("demo-north-buildings", unreal.Vector(-22800, -1000, 400), unreal.Vector(-22800, 3000, 300)),