Add per-row delete actions to the artifacts table

What does this MR do and why?

This MR adds row-level delete actions to the Artifact Registry repository detail page. Before this change, the artifacts table had no per-row actions. The only related control was the page-level Clear cache item on remote repositories. Now every artifact row has an Actions column with a kebab menu, so users can delete a single artifact from its row. The two repository kinds behave differently, because a cache eviction is recoverable on the next pull and a hosted delete is not. Both actions use one new GraphQL document calling the artifactRegistryArtifactDelete mutation, and the page refetches the repository detail and the artifact connection after the mutation instead of patching the cache, since the payload does not identify the affected row. This is Step 12 of the linked work item. The work item scoped the hosted row delete out, but it was requested for this MR.

• Remote repository row: "Delete cache entry" runs right away with no confirmation, then shows a toast.
• Hosted repository row: "Delete image" or "Delete package" opens a confirmation modal first, then shows a toast on confirm.

References

• #627582 (closed)

Screenshots or screen recordings

Before	After
TBD

How to set up and validate locally

1. Start a running Artifact Registry service, since the feature needs it.
2. Open a Rails console and run Feature.enable(:artifact_registry_ui).
3. Open an organization's Artifact Registry and open a repository detail page.
4. Open the kebab menu on an artifact row and check the action it offers.
5. On a remote repository row, choose "Delete cache entry" and confirm the toast appears.
6. On a hosted repository row, choose "Delete image" or "Delete package", check the modal text, confirm the delete, and check the toast.

MR acceptance checklist

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