M1: tune bot physics to stop launch/tip (playtest finding)

First 2-pilot test: bot was too hot (1200N cruise) and top-heavy -> launched
off on any nudge. Tamed in-scene: cruiseForce 1200->450, linearDamping 1.5,
angularDamping 6, maxAngularVelocity capped at 3, and lowered centerOfMass to
(0,-0.6,0) so it's bottom-heavy and resists cartwheeling. Added a host-only
debugAutoDriveFull flag on TreadPart to feel two-tread coordination solo.

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

Assets/Scripts/Bot/TreadPart.cs

@@ -80,6 +80,11 @@ namespace Jankenbots.Prototype
         [Range(0f, 0.5f)]
         public float leanDeadzone = 0.08f;
 
+        // ---- Debug / testing -----------------------------------------------------
+        [Header("Debug / testing")]
+        [Tooltip("HOST ONLY: when true, this tread ignores seat/input and drives at full cruise every FixedUpdate. Lets ONE machine feel two-tread coordination — the host auto-drives one tread while a friend/clone drives the other. Leave OFF for real play.")]
+        public bool debugAutoDriveFull = false;
+
         // The seat this tread maps to, resolved once from `side`.
         SeatManager.Seat MySeat => side == Side.Left ? SeatManager.Seat.Left : SeatManager.Seat.Right;
 
@@ -149,6 +154,15 @@ namespace Jankenbots.Prototype
             if (!IsServer) return;      // authority guard — clients never simulate
             if (chassis == null) return;
 
+            // Test affordance: drive full-forward regardless of seat/input, so one
+            // machine can feel two-tread coordination (host drives this tread, a
+            // clone/friend drives the other). Off for real play.
+            if (debugAutoDriveFull)
+            {
+                chassis.AddForceAtPosition(transform.forward * cruiseForce, transform.position, ForceMode.Force);
+                return;
+            }
+
             // Un-piloted tread goes limp: no pilot → no cached force. (Also clears any
             // stale input the instant a pilot leaves, so the bot doesn't coast on it.)
             if (_seats == null || _seats.PilotOf(MySeat) == SeatManager.NoPilot)