Fix cross-platform release smoke validation

[rusenask]

Summary

• evict the previously loaded platform image before each amd64/arm64 smoke run
• prevent Docker classic image-store digest collisions during architecture transitions
• assert per-platform eviction for the operator and both relay-agent variants

Evidence

• release run 34370156183 published the immutable staging image, passed amd64 execution, and failed before arm64 with cannot overwrite digest
• make release-workflow-test
• make test
• git diff --check

Release safety

No version tag, chart, latest tag, production test, or GitHub Release was promoted by the failed run.

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Note

Low Risk
CI/release-script smoke path only; no runtime operator behavior or promotion logic changes beyond safer local Docker cleanup during validation.

Overview
Release smoke validation now force-removes operator and agent images before each linux/amd64 / linux/arm64 pull-and-run cycle in verify_and_smoke, avoiding Docker classic store “cannot overwrite digest” failures when the same manifest-list digest is loaded for a second architecture.

The fake Docker harness records image rm invocations, and the image-release test asserts two forced removals per image (operator by digest, both relay-agent variants) across the dual-platform loop.

^{Reviewed by Cursor Bugbot for commit 6c4eba6. Configure here.}