#51 [Admin Panel] API Key Management - Rotate API Key

Implement POST /api/v1/admin/api-keys/<api_key_id>/rotate endpoint to rotate an API key. **API Specification:** - Endpoint: POST /api/v1/admin/api-keys/<api_key_id>/rotate - Permission Required: manage_users - Path Parameter: api_key_id (UUID) - Request Body: {grace_period_hours?: number} (default: 24) - Response: {api_key_id, new_api_key, old_key_expires_at, new_key_active_at} **Requirements:** - Generate new API key - Old key remains valid for grace period (default 24h) - Both keys work during grace period for zero-downtime rotation - New key shown ONLY once - Log audit event **Grace Period Logic:** - old_key_expires_at = now + grace_period_hours - During grace period, both old and new keys accepted - After grace period, old key automatically invalidated **IMPORTANT:** Implement with ultra attention to details and correctness. **BEFORE CLOSING:** Take screenshot showing API key rotation. Add comment summarizing implementation.