feat(experement): plan transfers with Pilz PTP instead of OMPL

- _contact transfer/approach and _retreat clear now use deterministic Pilz
  PTP joint interpolation; OMPL remains only the automatic fallback
- move_to_joints on the motion server tries PTP first, OMPL on failure
- verified in Webots execute mode: 1, 11, 14, 20 completed; no PTP failures
  in 1/11/14/20 server logs, OMPL used only as the fallback

src/iiwa_experement/test/test_operations.py

@@ -155,8 +155,8 @@ def test_take_tool_follows_the_visible_axial_route():
     assert bridge.attached == ['grant_vacuum']
     contact_goal = motion.moves[2][3]
     assert contact_goal.xyz == pytest.approx(expected.xyz, abs=1e-9)
-    assert motion.moves[0][1] == 'ompl'
-    assert motion.moves[1][1] == 'ompl'
+    assert motion.moves[0][1] == 'ptp'
+    assert motion.moves[1][1] == 'ptp'
     assert motion.moves[2][1] == 'lin'