fix(placement): both heights now come from a measurement after settling

The probe was armed from BeginPlay but the delay was lost when I removed the dead block, so
it never ran. Armed properly, three seconds after spawn, from the capsule's feet, on three
channels:

  GigLine foot Visibility after settling: actor Z 456, feet 369, hit Z 366

The character stands 3 cm above the road - the capsule skin - and the car sits at 367 on the
same measured surface with the model grounded on its wheels in Blender.

Both previous hand-tuned values were wrong, and wrong in opposite directions: the player
start did not need 561 (the capsule settles at 456), and the car had been placed at 342,
24 cm INTO the road, compensating for the wheel-grounding error that is now fixed. That is
the cost of tuning against a measurement taken while the pawn was still falling.

Tools/ue_build_demo_map.py

@@ -693,10 +693,11 @@ def build():
     # Same source: the vehicle's own downward trace in game reports the road under it at
     # Z 366, and the model is grounded in Blender (wheel bottoms at Z 0), so the panels sit
     # at 367 - one centimetre of clearance rather than a visible gap.
-    # 342, not the surface Z the pawn's trace reports (366): with the model grounded on its
-    # wheels the render still showed a ~25 cm gap at that height, so the visible road mesh
-    # and the traced surface disagree here. The number is empirical and says so.
-    vehicle_origin = unreal.Vector(-12950.0, -900.0, 342.0)
+    # Measured after settling: the ground under the car is Z 366 on every collision channel,
+    # and the model is grounded on its wheels in Blender, so the panels sit at 367. The
+    # earlier 342 was compensating for a grounding error that has since been fixed - it put
+    # the car 24 cm INTO the road.
+    vehicle_origin = unreal.Vector(-12950.0, -900.0, 367.0)
     vehicle_rotation = unreal.Rotator(pitch=0.0, yaw=0.0, roll=0.0)
 
     panel_systems = (