bot: fix slow/unsteerable driving + controls tooltip

Diagnosis (agent + live values): tuning & tread geometry were fine, debugAutoDrive
off — the real drag was the box chassis sliding on default ~0.6 friction, which ate
forward speed AND resisted yaw (dead steering).
- Bot_LowFriction physics material (0.3, Minimum combine) on the chassis → slides +
  yaws freely.
- TreadPart yaw-assist (220 N·m, sign reinforces natural differential) so a throttle
  difference gives a clear turn; cancels to zero on equal throttle (straight kept).
- SeatManager: context-aware controls tooltip under the seat box (on-foot vs driving),
  with a 'turn: differ vs teammate' hint.

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

Assets/Scenes/M1_Arena.unity

@@ -1639,12 +1639,18 @@ MonoBehaviour:
   m_Script: {fileID: 11500000, guid: cd21368c9a8b1064d913c375fb607c0b, type: 3}
   m_Name: 
   m_EditorClassIdentifier: Assembly-CSharp::Jankenbots.Prototype.CameraDirector
-  avatarOffset: {x: 0, y: 4, z: -6}
-  robotOffset: {x: 0, y: 8, z: -12}
+  avatarDistance: 8
+  robotDistance: 16
+  lookSensitivity: 0.18
+  zoomSensitivity: 4
+  minDistance: 3
+  maxDistance: 80
+  minPitch: -8
+  maxPitch: 78
+  lookHeight: 1.2
   orbitRadius: 20
   orbitHeight: 9
   orbitSpeed: 18
-  lookHeight: 1.2
 --- !u!1001 &579422633
 PrefabInstance:
   m_ObjectHideFlags: 0
@@ -3441,7 +3447,7 @@ BoxCollider:
   m_PrefabInstance: {fileID: 0}
   m_PrefabAsset: {fileID: 0}
   m_GameObject: {fileID: 781174154}
-  m_Material: {fileID: 0}
+  m_Material: {fileID: 13400000, guid: 6c687d24b6f5fbb4783d28d635f71a29, type: 2}
   m_IncludeLayers:
     serializedVersion: 2
     m_Bits: 0
@@ -5564,6 +5570,7 @@ MonoBehaviour:
   chassis: {fileID: 0}
   cruiseForce: 450
   throttleDeadzone: 0.08
+  yawAssistTorque: 220
   pivotAnchorStrength: 1500
   pivotAngularResistance: 400
   leanTorque: 500
@@ -5699,6 +5706,7 @@ MonoBehaviour:
   chassis: {fileID: 0}
   cruiseForce: 450
   throttleDeadzone: 0.08
+  yawAssistTorque: 220
   pivotAnchorStrength: 1500
   pivotAngularResistance: 400
   leanTorque: 500