fix: car now drives - collision groups, rigid hubs, pad spawn, anticheat grace

Four independent bugs kept the car immobile at the world origin:

1. Wheels collided with their own chassis. Wheel inner edge sits at 2.80
   vs body edge 3.00, and wheel top -0.20 vs body bottom -0.70. The
   overlap is intentional styling, but in one collision group the wheels
   ground against the body: motors spun ~1 rad/s against 20,000 torque.
   Wheels now use a CarWheel group that ignores CarChassis.

2. Suspension exploded on spawn. PrismaticConstraint+SpringConstraint
   between a 0.6-stud hub and the ballasted body was unstable enough to
   fling knuckles ~10,000,000 studs out, past FallenPartsDestroyHeight,
   deleting the wheels. Replaced with a rigid welded hub mount.

3. Car spawned at world origin, not the pad. MapBuilder made a SpawnPad
   part but no SpawnLocation, so characters spawned at (0,0,0) and Sit()
   dragged the car to them. Added a real SpawnLocation and the model is
   now pivoted after parenting, with the character teleported first.

4. AntiCheat snapped that legitimate spawn teleport back. An ~8,500-stud
   server move reads as a teleport hack. Added AntiCheat.grant() so
   server-initiated moves are exempt for a short grace window.

Verified in Studio: 881 studs in 6s, 496 studs/s top speed, 152 deg
steering, braking 33 -> 0 studs/s, chassis stays upright.

c1_georeference.json

@@ -0,0 +1,29 @@
+{
+  "note": "C1 world<->real Tokyo georeference. X IS NEGATED vs source data.",
+  "world_to_real": {
+    "lon": "139.75654 + 2.528e-06*(-X)",
+    "lat": "35.67327 + 2.117e-06*Z"
+  },
+  "real_to_world": {
+    "X": "-(lon-139.75654)/2.528e-06",
+    "Z": "(lat-35.67327)/2.117e-06"
+  },
+  "orientation": {
+    "+Z": "NORTH",
+    "-Z": "SOUTH",
+    "-X": "EAST",
+    "+X": "WEST"
+  },
+  "scale_studs_per_meter": 4.3,
+  "median_error_m": 366,
+  "loop_center_world": [
+    180,
+    -180
+  ],
+  "verified": [
+    "Nihonbashi east of Palace",
+    "Tokyo Tower SW outside loop",
+    "Ginza/Tsukiji east",
+    "Nagatacho/Kasumigaseki west"
+  ]
+}