fix(release): harden v0.9 image bases

[jeremi]

Summary

Refresh the pinned Node 22 and distroless Debian 12 runtime bases used by the v0.9 release images.

Remove npm and npx from the source-adapter sidecar image. The runtime invokes Node.js directly for the bundled mock registry server and never installs packages, so retaining npm only expands the release image and its advisory surface.

Why

The beta-11 release-candidate Grype pass found high-severity advisories with available fixes in the old Relay base and in npm packages bundled into the sidecar base. Release policy requires fixing patched same-major dependencies before the prepare release PR merges.

Verification

• release helper unit suite: 42 passed
• all three release Dockerfile secret-copy checks passed
• rebuilt the sidecar and Relay images as Linux/amd64 from the exact beta-11 candidate binaries
• confirmed Node.js v22.23.1 remains available in the sidecar
• confirmed npm and npx are absent
• rescanned immutable local-registry digests with the release workflow versions of Syft and Grype
• zero high or critical findings with an available fix remain across the Notary, sidecar, and Relay candidate images
• git diff --check passed

This PR must merge before #340 is refreshed and merged.

[jeremi]

Maintainer security review record:

• Scope is limited to the two release runtime Dockerfiles.
• The refreshed base references are immutable sha256 digests.
• The sidecar still provides Node.js for the bundled mock registry server, while unused npm/npx tooling is absent.
• Linux/amd64 images were rebuilt from the exact beta-11 candidate binaries and scanned by immutable local-registry digest with the release workflow versions of Syft and Grype.
• Across Notary, sidecar, and Relay, zero high or critical matches with an available fix remain after this change.
• Remaining base-image findings have no packaged fix and remain review evidence. This is not a zero-CVE claim.
• The release Dockerfile secret-copy assurance check and release helper suite pass.
• No authentication, authorization, audit, disclosure, replay, approval, config-trust, or signing invariant is changed.

Security review result: approve this prerequisite after required CI completes.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Exclude npm from final image layers

For the release image pushed from this Dockerfile, deleting /usr/local/lib/node_modules/npm in a later RUN step only adds whiteouts over files that already came from the node:22-bookworm-slim base layer. The npm package tree is still present in the distributed image blobs and can be recovered or reported by scanners that inspect all layers, so this does not actually keep npm out of the image as the hardening comment requires. Build the final stage from a base/layer that never contains npm, or copy only the needed Node runtime files into a fresh final stage.

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