Push agent_artifacts_page flag on project settings edit page

What does this MR do and why?

The Store AI audit events toggle in gitlab_duo_settings.vue is conditionally rendered behind glFeatures.agentArtifactsPage && showAllSettings, but the agent_artifacts_page feature flag was never pushed to the frontend in EE::ProjectsController, which backs the project's Settings > General (edit) action.

This MR adds push_frontend_feature_flag(:agent_artifacts_page, @project.root_ancestor, type: :beta) to the before_action only: [:edit] block in EE::ProjectsController, making the toggle visible on the project-level GitLab Duo settings section, consistent with the group-level behavior.

References

• Related to https://gitlab.com/gitlab-org/gitlab/-/issues/606950

Screenshots or screen recordings

Before	After
Toggle absent from project Settings > General > GitLab Duo

How to set up and validate locally

1. Enable the agent_artifacts_page feature flag:

   Feature.enable(:agent_artifacts_page)

2. Navigate to a project's Settings > General, expand the GitLab Duo section.
3. Confirm the Store AI audit events toggle is now visible under the Data and privacy section.

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.