ci: retry stale ArtifactHub metadata

[KeiaiLab-PHIL]

Summary

• retry ArtifactHub package metadata mismatch, not only 404, so signed=false stale tracker state can converge after signed OCI republish
• keep final error explicit when metadata never reaches version/appVersion/repository/signed=true

Validation

• bash -n hack/artifacthub_smoke.sh hack/artifacthub_smoke_test.sh
• bash hack/artifacthub_smoke_test.sh
• git diff --check
• TAG=1.12.4 ARTIFACTHUB_SMOKE_ATTEMPTS=2 ARTIFACTHUB_SMOKE_SLEEP_SECONDS=1 bash hack/artifacthub_smoke.sh (expected current live stale metadata retry then failure while ArtifactHub still reports signed=false)