Add split-button dropdown [Export ▼] on EngagementDetailPage that
downloads engagement as Markdown, CSV, or PDF via
GET /api/engagements/<id>/export?format=md|csv|pdf.
Both halves open the dropdown (no default left-click action).
RBAC-gated with canEditEngagements (admin + redteam only).
Loading state per item, toast on error, click-outside + Escape close.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
100441bdeb