M1: wire shove ball + follow camera into M1_Arena

- ShoveBall: in-scene NetworkObject sphere (1.5m, 10kg, drag 0.5) at
  (0,0.75,6), host-authoritative via NetworkRigidbody/NetworkTransform,
  ShoveBall.physicsMaterial (friction 0.4/0.5, bounce 0.3). No script.
- FollowCamera on Main Camera, target=Bot, offset (0,8,-12).
- Solo host smoke test passed: ball spawns + rests on ground + shoves;
  camera frames the bot.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/Physics/ShoveBall.physicsMaterial

@@ -0,0 +1,15 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!134 &13400000
+PhysicsMaterial:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_Name: ShoveBall
+  serializedVersion: 2
+  m_DynamicFriction: 0.6
+  m_StaticFriction: 0.6
+  m_Bounciness: 0
+  m_FrictionCombine: 0
+  m_BounceCombine: 0