Move the setup instructions entry point into the page header

What does this MR do and why?

This MR moves setup instructions from the kebab menu to a dedicated button in the page heading, on the Artifact Registry repository detail page.

• Adds a "Setup instructions" button to the page heading, placed before Edit. (address #613241 (comment 3685382498))
• Removes "View setup instructions" from the kebab menu. The kebab keeps "Copy repository URL" and "Delete repository".
• Shows the button only when a client URL can be built, same condition the kebab item used before.
• Hides the button on a hosted repository with no artifacts. That empty state already shows the same setup steps inline.
• Keeps the button on a remote repository. Remote repositories have no such empty state.
• Adds a kind prop to the drawer. Hosted repositories get Install and Publish tabs. Remote repositories get Install only, since nothing publishes to a remote repository.
• Shares one translated string, SETUP_INSTRUCTIONS_TITLE, between the button label and the drawer title.
• Restyles the code snippets in the drawer: rounded corners, subtle background, even spacing, smaller section headings.
• Regenerates locale/gitlab.pot. Drops the string ArtifactRegistry|View setup instructions.
• Touches the hosted repository page as part of this remote work slice. The issue accepts this. A remote-only button would leave the hosted page with both a kebab item and a button for the same content.

References

• Issue (this MR does Step 4): #627312 (closed)
• Parent epic: gitlab-org#22453
• Sibling MR (Step 9): !253142 (merged)

Ordering: this MR and the Step 9 MR both branch off master and merge cleanly in either order. Until the Step 9 MR merges, an empty remote repository shows both the old empty state and the new button. That resolves once it lands.

Screenshots or screen recordings

What	Screenshot
Setup instructions button
Show only Install tab for remote repositories & styling changes
code-block border and background changes

This change is behind the default-off artifact_registry_ui feature flag.

How to set up and validate locally

1. Enable the artifact_registry_ui feature flag.
2. Open the Artifact Registry repository list for an organization.
3. Open a hosted repository and check the setup instructions button and drawer.
4. Open a hosted repository with no artifacts and confirm the button is hidden.
5. Open a remote repository and check the button shows with an Install-only drawer.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

• No changelog entry. The artifact_registry_ui flag is default off.
• Jest specs updated in repository_header_spec.js, repository_actions_spec.js, setup_drawer_spec.js, and repository_detail_spec.js. All 52 suites and 1755 tests pass in ee/spec/frontend/packages_and_registries/artifact_registry.
• ESLint and Prettier clean.
• No docs change. The Artifact Registry UI is not documented yet.
• No database, security, or migration surface.
• Strings externalized. locale/gitlab.pot regenerated.