[rg3122]

Summary

When a source object stops matching a controller shard's watch label selector, the previous shard may receive a NotFound response while its local artifact directory still exists. This can leave stale artifacts on disk and mask sharding misconfigurations.

This change cleans up the local artifacts when reconciliation encounters a missing object across the Bucket, GitRepository, HelmChart, HelmRepository, and OCIRepository controllers.

• Adds a shared helper to safely resolve and remove the object's artifact directory.
• Retries reconciliation if artifact cleanup fails.
• Adds a unit test verifying that only the target object's artifacts are removed and unrelated artifacts are preserved.

Fixes #2150

Validation

• Added unit test: TestRemoveArtifactsForMissingObject
• Full Go test suite has not been run; CI validation is still required.