Nsight: Add Nsight Compute service and jupyter-server-proxy config

[brycelelbach]

Changes

• Use jupyter-server-proxy instead of the Nsight JupyterLab Plugin to display Nsight Streamer.
• Add Nsight Compute (ncu) service alongside the existing Nsight Systems (nsys) streamer.
• Add .turn-credentials to .gitignore.
• Only generate alphanumeric passwords for the TURN server.
• Guard Nsight Systems config copy in the nsight entrypoint so it doesn't fail on containers that don't ship it (e.g. the ncu streamer).
• Handle TURN_PORT env var in entrypoint-nsight.bash for the ncu service (uses port 3479 to avoid conflict with nsys on 3478).
• Rename NSIGHT_HTTP_URL to NSYS_HTTP_URL in plugin settings generation.
• Update TURN credentials comment to reference nsys, ncu, and jupyter services.