ProblemDetails.Status not populated on error responses

The `ProblemDetails` bodies produced by the result→HTTP conversions omit the `Status` member for several statuses, so the JSON body's `status` is `null` even though the HTTP status code on the response is correct. It is also applied inconsistently — some builders set it, others don't — and RFC 7807 §3.1 says the `status` member SHOULD be present and match the actual HTTP status code.

| Result status | Minimal API (`MinimalApiResultExtensions`) | MVC (`ResultStatusMap`) |
|---|---|---|
| 422 Error / 404 NotFound / 409 Conflict | missing | missing |
| 500 CriticalError / 503 Unavailable | set | missing |
| 403 Forbidden / 401 Unauthorized | set | n/a (status code only, no body) |

This matters to clients that read `status` off the parsed body (e.g. generated clients that throw the parsed `ProblemDetails`), where the HTTP status code is otherwise not readily available.

Happy to open a PR.

Start by locating MinimalApiResultExtensions and ResultStatusMap, then trace the result-to-HTTP conversions for the statuses listed in the issue. Verify each produced ProblemDetails JSON body has a status matching the HTTP response code, including 422, 404, 409, 500, and 503.

Written by the indexing model from the issue text.