Docker: enable GUI forwarding from container (Qt/xcb + Open3D)

[kvnptl]

What

• Dockerfile: Install X11/xcb and related libs so OpenCV’s Qt backend can show windows when using host X11 forwarding (cv2.imshow). Adds libsm6 (fixes missing libSM.so.6), plus libx11-xcb1, libxcb-*, libxext6, etc. Uses libxcb-sync1 for Ubuntu 22.04 (not libxcb-sync0).
• Dockerfile: ENV PATH=$PATH:/opt/conda/envs/my/bin, modern ENV form (silences Docker LegacyKeyValueFormat warning).
• run_container.sh: set XDG_RUNTIME_DIR + create /tmp/runtime for Open3D; QT_X11_NO_MITSHM=1; optional QT_DEBUG_PLUGINS=0.

Why

Without these system libraries, Qt fails to load the xcb platform plugin inside the container even with DISPLAY and /tmp/.X11-unix mounted. Open3D may error if XDG_RUNTIME_DIR is unset.

How to verify

1. On host: xhost +local:root
2. Build image, run bash docker/run_container.sh
3. Run a script that uses cv2.imshow and/or Open3D visualization -> windows should appear on the host.