Confirms (captures) an approved order, moving it to Confirmed. Requires scope orders:write.

Example response (200):

{ "success": true, "code": "SUCCESS", "data": { "id": "0d3f...e823", "status": "Confirmed", "confirmedAt": "2026-06-11T09:30:00Z" } }

Errors: 400 INVALID_STATUS if the order can't be confirmed in its current state,
404 NOT_FOUND if the order doesn't exist or isn't yours.