Filter a priority web queue

`$match` can combine several field conditions. A document continues only when every condition in the match object is satisfied, including comparison queries such as `$gte`.

Return completed web orders worth at least 150. Shape each result to `orderId`, `region`, and `total`, then sort largest first.

Expected result: A descending priority queue with exactly three fields per document.

[
  { $match: { status: "completed", channel: "web" } }
]