feat(audit-events): expose Audit Events (Premium/Ultimate)

[polaz]

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Problem

GitLab Audit Events expose who did what, when — instance/group/project scoped. Premium+ feature, useful for compliance investigations. We don't expose any audit-events tool.

Investigation done (current state)

Verified against src/entities/:

• ❌ grep -ri 'audit.*event' src/ returns 0 hits

Re-verify before coding:

grep -rIni 'audit' src/entities/
ls src/entities/ | grep audit

Acceptance criteria

• New entity src/entities/audit_events/ with read-only browse_audit_events actions:
  • list_instance (admin-only, GET /audit_events)
  • list_group (Premium+, group owner/admin)
  • list_project (Premium+, project owner/admin)
  • get (single audit event)
• Tier-gated: Premium+ for group/project, Ultimate for some advanced filters
• No write actions (audit events are immutable by design)
• Integration test gated via describeIfTier('premium', ...)

GitLab API

• Endpoints: /audit_events (instance), /groups/:id/audit_events, /projects/:id/audit_events
• Tier: Premium/Ultimate
• Docs: https://docs.gitlab.com/api/audit_events/

Estimate

1d

Context

Found during GitLab 18→19 API landscape analysis.