ci: nudge ArtifactHub repository tracking

[KeiaiLab-PHIL]

Summary

• when ArtifactHub API credentials are available, send a repository update before smoke polling
• this gives workflow_dispatch verification a non-destructive tracker nudge after signed OCI chart backfills
• passive retry remains the fallback when credentials are absent

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)