Add AI Governance Dashboard tab scaffold behind FF

What

Frontend scaffold for the AI Governance Dashboard (beta). Adds a feature-flagged Dashboard tab to the existing GitLab Duo → Governance settings page (group and project level), with a summary header and placeholder cards: AI Agents, AI Sessions, Audit Trail, AI Agent Inventory.

Behind ai_governance_dashboard FF.

References

• Related issue https://gitlab.com/gitlab-org/gitlab/-/work_items/604505
• Planning issue: https://gitlab.com/gitlab-org/gitlab/-/work_items/603776
• Beta epic: gitlab-org#21306

Screenshots

Before (with FF disabled)	After (with FF enabled)

For Projects

How to verify this locally

1. Set up GitLab Duo locally (SaaS mode + licensed group): see Set up GitLab Duo for local development.
2. Enable the flag: Feature.enable(:ai_governance_dashboard)
3. Visit Settings → GitLab Duo → Governance on the gitlab-duo group and open the Dashboard tab.