feat: add release-to-move TCP gizmo control in Webots

Add a native Webots marker for setting the active tool's TCP position and
orientation. Dragging edits the preview; releasing the mouse submits one
complete, checked joint trajectory with configured TCP speed limits.
Unreachable targets reset the marker to the current TCP.

Preserve coordinate, joint, and control-file commands through motion
reservations and a controller action proxy. Give the gizmo lowest priority
and finish its committed trajectory before dispatching queued regular
commands, including waits longer than the former two-second service timeout.

Place the patron TCP at its working end, 55.2 mm along local Z, and use the
flange TCP when no tool is attached. Add digital_twin.tcp_gizmo configuration,
ROS interfaces, launch integration, and regression coverage.

Document operation, configuration, tool attachment, speed limits, and
troubleshooting in both Russian and English.

Validation: 42 Python tests and 8 C++ tests passed. Webots regressions covered
one action per release, translation and rotation with and without a tool,
unreachable targets, and ordinary commands waiting for gizmo completion.

src/iiwa_msgs/CMakeLists.txt

@@ -7,6 +7,9 @@ find_package(geometry_msgs REQUIRED)
 find_package(action_msgs REQUIRED)
 
 rosidl_generate_interfaces(${PROJECT_NAME}
+  "msg/GizmoCommand.msg"
+  "msg/GizmoState.msg"
+  "srv/MotionPriority.srv"
   "srv/MoveToPose.srv"
   "srv/MoveToNamedPose.srv"
   "action/MoveToPose.action"

src/iiwa_msgs/msg/GizmoCommand.msg

@@ -0,0 +1,3 @@
+# One committed TCP target on mouse release, with generation from GizmoState.
+geometry_msgs/PoseStamped target
+uint64 epoch

src/iiwa_msgs/msg/GizmoState.msg

@@ -0,0 +1,6 @@
+# Actual TCP pose; enabled is false while any higher-priority motion owns control.
+geometry_msgs/PoseStamped actual
+bool enabled
+# Advances on rejection, controller completion, or higher-priority ownership.
+uint64 epoch
+string reason

src/iiwa_msgs/srv/MotionPriority.srv

@@ -0,0 +1,7 @@
+# Acquire/renew or release a named high-priority lease. TTL uses wall time [s].
+string owner
+bool acquire
+float64 ttl
+---
+bool success
+string message