#53 [Admin Panel] Invitation System - List Invitations

Implement GET /api/v1/admin/invitations endpoint to list all invitations. **API Specification:** - Endpoint: GET /api/v1/admin/invitations - Permission Required: manage_users - Query Parameters: status (pending, accepted, expired, cancelled), page, per_page - Response: {data: invitations[], pagination: {...}} **Response Fields:** - invitation_id, email, roles[] - status, created_at, expires_at - created_by_email, message - accepted_at (if accepted) **Requirements:** - Filter by status - Sort by created_at desc - Show expired invitations - Include resend count **IMPORTANT:** Implement with ultra attention to details and correctness. **BEFORE CLOSING:** Take screenshot showing invitations list. Add comment summarizing implementation.