fix(site): slice the road too - the 2 m lid was a convex hull, not geometry

The road was never mis-modelled: a 279 m strip imports with ONE auto-generated convex hull, and a
convex hull's top is the strip's maximum height. A downward trace therefore landed at 366 cm - a flat
lid about 2 m above the visible road, which sits at roughly 152 cm there. That single fact explains
every failed sidewalk fix, the 'road above its own sidewalk' reading, and why the player always ended
up on Road_Hollywood.

Slicing the road the way the sidewalks already were fixes it, and the cross-section is now continuous:

  Terrain_DEM       154
  Sidewalk_North_07 158
  Road_Hollywood_07 158   (was 366)

Two changes had to land together: the road exported in slices, and the map stopped staging the single
Road_Hollywood asset - which still sat on top of the slices and won every trace until removed.

All 23 captures regenerated; the player and the car both stand on a continuous ground plane.

Art/blender/site/export_site_fbx.py

@@ -26,7 +26,12 @@ MESHES = ("Terrain_DEM", "Road_Hollywood", "Sidewalk_South", "Sidewalk_North",
 # its bounding box is the highest point anywhere along the street, which is 2.2 m above the
 # surface at the player's position, and that misled every placement decision in the demo.
 # A 20 m slice has a bounding box that means something where it stands.
-SEGMENTED = ("Sidewalk_North", "Sidewalk_South", "Kerb_North", "Kerb_South")
+# The road is sliced for the same reason as the sidewalks: a 279 m strip imports with a single
+# convex hull whose top is the strip's MAXIMUM height, so a downward trace anywhere on it lands on
+# that hull - a flat lid 2 m above the visible surface. A 20 m slice has a hull that follows the
+# surface it belongs to.
+SEGMENTED = ("Sidewalk_North", "Sidewalk_South", "Kerb_North", "Kerb_South",
+             "Road_Hollywood")
 SEGMENT_M = 20.0