Fix PrismaticJoint (trunk) control: IdealPDActuator with high stiffness

Replace ImplicitActuator (which doesn't work for prismatic joints) with
IdealPDActuator. This bypasses PhysX drive and explicitly computes PD forces
using set_dof_actuation_forces().

Changes:
- stiffness=100k, damping=5k to resist arm reaction forces (~150N) with <2mm deflection
- Read trunk_cmd from ArticulationCfg initial position (single source of truth)
- Integrate trunk diagnostics into robot state output
- Remove hardcoded trunk_target parameter

scripts/environments/teleoperation/xr_teleop/diagnostics.py

@@ -21,9 +21,10 @@ class DiagnosticsReporter:
             jnames = robot.joint_names
             self._left_arm_idx = [i for i, n in enumerate(jnames) if n.startswith("l_joint")]
             self._right_arm_idx = [i for i, n in enumerate(jnames) if n.startswith("r_joint")]
+            self._trunk_idx = jnames.index("PrismaticJoint") if "PrismaticJoint" in jnames else None
 
     def report(self, env, obs, frame: int, last_act: np.ndarray | None = None,
-               xr_client=None, read_gripper_contact=None):
+               xr_client=None, read_gripper_contact=None, trunk_target: float | None = None):
         """Print diagnostics if frame is on interval boundary."""
         if frame % self.interval != 0:
             return
@@ -77,6 +78,12 @@ class DiagnosticsReporter:
             print(f"| Cmd right_arm(abs):         {last_act[12:19]}")
             print(f"| Cmd right_gripper:          {last_act[19:]}  (+1=open -1=close)")
             print(f"| Joystick (x=turn,y=fwd):    {joy_str}")
+            if self._trunk_idx is not None:
+                trunk_pos = robot.data.joint_pos[0, self._trunk_idx].item()
+                trunk_vel = robot.data.joint_vel[0, self._trunk_idx].item()
+                trunk_force = robot.data.applied_torque[0, self._trunk_idx].item() if hasattr(robot.data, 'applied_torque') else float('nan')
+                trunk_tgt_str = f"{trunk_target:.4f}" if trunk_target is not None else "N/A"
+                print(f"| Trunk pos={trunk_pos:.4f}  vel={trunk_vel:.6f}  target={trunk_tgt_str}  force={trunk_force:.2f}")
             print(f"----------------------------------------------------------------")
         else:
             eef_pos = policy_obs["eef_pos"][0].cpu().numpy()