0.5.4 - Residual CVE pass

Residual CVE pass. No application code, dependency pin, or CUDA change. Local Trivy scan of the candidate image: zero CRITICAL or HIGH fixable findings on every target.

• libnghttp2-14 pulled to the focal-security build in the existing apt layer.
• The mambaforge bootstrap environment under /opt/conda, which the service never runs, had 2023-era certifi, cryptography, pyOpenSSL, setuptools and urllib3. They are upgraded in place with that environment's own pip, followed by a pip check.
• The remaining msgpack and setuptools findings were pip's own vendored copies, declared in pip's bundled software bill of materials, not installed packages. pip is removed from the finished image; nothing at runtime uses it, and the hotfix overlay (Dockerfile.release) does not need it either.

Validated on the GPU host against the reference file before release; per-pass numbers are in docs/SESSION_KNOWLEDGE.md.