Install PyHPC profiler kernels in Jupyter search path

[robobryce]

Summary

Install the Nsightful kernelspecs under /usr/local/share/jupyter/kernels, make them readable/traversable by non-root users, and verify during the Docker build that an unprivileged user can discover both kernels.

Failure fixed

Event-head PyHPC CI run 30199357352 failed because the base test container could not find nsightful-nsys or nsightful-ncu. Inspection of the published image showed that nsightful install --sys-prefix placed the kernels under /usr/share/jupyter/kernels with root-owned 0700 directories. The non-root CI user could not traverse them.

Validation

• inspected the exact published image layer and confirmed the old root-owned 0700 kernelspec directories
• the Docker build now checks kernel discovery using the unprivileged nobody user
• pre-commit and commit-signature checks pass
• full CI image rebuild/test required because this changes the Docker image

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[github-actions]

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[robobryce]

Additional exact regression proof:

• extracted the kernelspec layer from the published 9ab4e66 PyHPC image
• mounted the kernels under /usr/local/share/jupyter in a clean Python container running as UID/GID 65534
• with the original root-owned 0700 directory modes, KernelSpecManager().get_all_specs() returned []
• after the PR's chmod -R a+rX, the same non-root query returned ['nsightful-ncu', 'nsightful-nsys']

This directly reproduces the CI failure and validates the permissions portion of the fix.