Add ROS2 publisher and subscriber to MessageHandlerNode

[andyvn1]

Wire up the communication between message_handler_node and the motion planner node:

• Publisher on /key_to_press (std_msgs/String) — sends one character at a time
• Subscriber on /key_press_result (std_msgs/Bool) — receives success/fail from motion planner
• Publisher on /typing_status (std_msgs/String) — broadcasts current status for C2 display
  Acceptance criteria: node starts without errors and topics are visible in ros2 topic list