Mecanum Webots via Supervisor kinematic injection

Replace the failing ODE-rolled mecanum chassis dynamics with a
Supervisor.setVelocity call that uses the gym mecanum forward
kinematics formula directly. Wheel motors still spin (visual);
chassis motion comes from the gym model so training and deployment
match by construction.

Results (seed=42, n=10 sheep): BC + RL mecanum pen 10/10 in both
field and field_round. n=5 mecanum cells still 0/5 due to tracker
phantoms anchored to wall corners under the 360° LiDAR — documented
in docs/status.md as the remaining gap.

Cleanup: drop deploy-time hacks (HERDING_HEADING_*, HERDING_OMEGA_CLAMP,
HERDING_TRACKER_*) that were workarounds for the old ODE chaos;
revert the proto inertiaMatrix, roller dampingConstant, and reduced
motor torque since they no longer carry load; refresh comments
around the mecanum config presets.

training/bc/collect.py

@@ -179,19 +179,26 @@ def main():
               f"'{FIELD_SHAPE}'. This should not happen — file a bug.")
 
     from herding.config import (
-        HerdingConfig, HERDING_WEBOTS, HERDING_MEC_WEBOTS,
+        HerdingConfig, HERDING_WEBOTS, HERDING_MEC_WEBOTS, HERDING_MEC_WEBOTS_360,
         DomainRandomConfig, RobotConfig,
     )
     if args.use_webots_preset:
-        # Pick the drive-matched Webots preset — for mecanum we use the
-        # variant that simulates the physical-roller proto's strafe
-        # efficiency and forward bleed so the policy trains under the
-        # same imperfect kinematics it sees at deployment.
-        base = HERDING_MEC_WEBOTS if args.drive_mode == "mecanum" else HERDING_WEBOTS
+        # Mecanum uses the 360° preset (the deployable mecanum target);
+        # diff drive keeps the canonical 140° preset.
+        if args.drive_mode == "mecanum":
+            base = HERDING_MEC_WEBOTS_360
+            preset_name = "HERDING_MEC_WEBOTS_360"
+        else:
+            base = HERDING_WEBOTS
+            preset_name = "HERDING_WEBOTS"
+        # Small compass noise for mecanum training (robustness margin
+        # for the Webots compass sensor).
+        compass_std = 0.1 if args.drive_mode == "mecanum" else 0.0
         herding_cfg = base.replace(
             domain_random=DomainRandomConfig(
                 fp_rate=args.fp_rate,
                 wheel_slip_std=args.wheel_slip_std,
+                compass_noise_std=compass_std,
             ),
             robot=RobotConfig(
                 action_smooth=args.action_smooth,
@@ -199,10 +206,10 @@ def main():
                 strafe_to_forward_bleed=base.robot.strafe_to_forward_bleed,
             ),
         )
-        preset_name = "HERDING_MEC_WEBOTS" if args.drive_mode == "mecanum" else "HERDING_WEBOTS"
         print(f"[demos] {preset_name} preset + DR: fp_rate={args.fp_rate} "
               f"action_smooth={args.action_smooth} wheel_slip_std={args.wheel_slip_std} "
-              f"strafe_eff={herding_cfg.robot.strafe_efficiency:.2f}")
+              f"strafe_eff={herding_cfg.robot.strafe_efficiency:.2f} "
+              f"compass_noise={compass_std}")
     else:
         herding_cfg = None
         if args.fp_rate > 0.0 or args.action_smooth > 0.0 or args.wheel_slip_std > 0.0: