feat(Car): wire NWH Vehicle Physics 2 — scripts only, scene/prefabs still TODO

Code-only first pass. The local Player.prefab (ball) is still in the scene
until the user creates the PlayerCar / RemoteCar prefab variants in the Editor.

New scripts:
- VehicleLocalSetup: attaches name label + colored capsule marker to the local
  vehicle, registers its Rigidbody with NetworkManager for broadcast.
- RemoteVehicleSync: snapshot interpolation for remote vehicles. Disables the
  NWH VehicleController + every WheelController + every AudioSource on init.
  Makes the rigidbody kinematic, MovePosition-driven from network. Disables all
  non-trigger colliders during the 1.5s spawn grace window to avoid ejecting
  overlapping locals at connect.

Adapted scripts:
- NetworkManager: RegisterLocalVehicle(Transform, Rigidbody) replaces the
  FindFirstObjectByType<PlayerController>() lookup. Remote spawn now wires
  RemoteVehicleSync instead of RemotePlayerController.
- LobbyUI: OnConnected drives VehicleLocalSetup.SetupLocal; OnDisconnected
  toggles NWH.VehicleController instead of PlayerController.
- GameManager.SetPlayerActive: toggles VehicleController, not PlayerController.
- DebugNetworkUI: live position read from VehicleController.vehicleRigidbody.
- ChatUI: drops PlayerController.ResetInputs() (NWH polls Input System each
  frame; no manual reset needed when chat opens).
- StatsTracker: drops dead _pc field; Rigidbody still gets resolved via
  GetComponent on the host GameObject (will be the vehicle on Car).

Frontend (deployed earlier on master): build_ball replaces pretty_build assets.

game/Assets/Scripts/Network/DebugNetworkUI.cs

@@ -116,12 +116,12 @@ public class DebugNetworkUI : MonoBehaviour
         if (state != null)
             ImGuiSkin.DrawField("Server Pos", $"({state.x:F1}, {state.y:F1}, {state.z:F1})");
 
-        var pc = FindFirstObjectByType<PlayerController>();
-        if (pc != null && pc.isActiveAndEnabled)
+        var vehicle = FindFirstObjectByType<NWH.VehiclePhysics2.VehicleController>();
+        if (vehicle != null && vehicle.isActiveAndEnabled)
         {
-            var pos = pc.transform.position;
+            var pos = vehicle.transform.position;
             ImGuiSkin.DrawField("Live Pos", $"({pos.x:F1}, {pos.y:F1}, {pos.z:F1})");
-            var rb = pc.GetComponent<Rigidbody>();
+            var rb = vehicle.vehicleRigidbody;
             if (rb != null)
             {
                 var v = rb.linearVelocity;