Add um982_driver + gnss_comm (renamed from rtk_ws to fhd_rtk_ws)

UM982 RTK GNSS driver workspace used by the triple-camera scan GUI for
recording /ublox_driver/receiver_pvt alongside LiDAR/camera bags. Ported
from FAST-LIVO2-RTK-ROS2's um982_driver spec, adapted for this UM982
receiver instead of the original repo's GNSS module.

.gitignore

@@ -0,0 +1,7 @@
+# colcon build artifacts — regenerate with `colcon build`
+build/
+install/
+log/
+
+__pycache__/
+*.pyc