Ray dashboards won't load due to symlinked files during install

[roclark]

Describe the bug

Trying to open the Ray dashboard in the NeMo-RL container will result in 404 errors and the dashboard will never load. This is due to Ray being installed in the /opt/nemo_rl_venv directory by uv but the main.js and main.css files used for the Ray dashboard get symlinked to /root as the container install does symlinks for all copies in the uv stages in the Dockerfile. The HTTP server used by Ray dashboard doesn't allow symlinks outside of the parent directory which causes the 404 errors. Instead, by using the copy link-mode during the uv pip install for Ray will fix the error.

Steps/Code to reproduce bug

1. Build the nemo-rl release container locally. Tested with commit 5514d1e6eb0036f4ccbc5dac42b1b860959d0087.
2. Launch the container locally and expose port 8265 for the Ray dashboard.
3. Run ray start --head --port=6379 --dashboard-host=0.0.0.0 --block --include-dashboard=true inside the container to start the Ray cluster.
4. Open localhost:8265 in your browser to view the Ray dashboard - this will never load and there will be 404 errors in the browser debug tools.

Instead, this can be worked around by re-installing the ray package with uv and using copy link-mode. To do so:

1. Stop the Ray process in the container if still running.
2. Re-install ray with uv pip install --link-mode=copy --force-reinstall "ray[default]==2.46.0".
3. Re-launch the Ray cluster with ray start --head --port=6379 --dashboard-host=0.0.0.0 --block --include-dashboard=true.
4. Open localhost:8265 in your browser - the dashboard should now load properly.

Expected behavior

Ray should be installed without symlinks so it can render the dashboard properly. As-is, the dashboard will not load due to the symlinks being in another parent directory.

The Dockerfile should be updated to either force-reinstall Ray without symlinks, or all dependences should be installed without symlinks, but that is less desirable.