Resolve the effective price for an item + account (company tier → base price) on a given date. <br>`asOf` is required, and is a System.DateOnly. It used to be an optional System.DateTime, which made this the one place in the feature where the answer depended on where the question was asked from — twice over. Omitted, the server substituted its own UTC date, so a caller in UTC+3 asking at 01:00 local was answered for the previous day. Supplied with an offset, query-string binding converted it to universal time, so `2026-08-01T00:00:00+03:00` resolved prices as of `2026-07-31T21:00Z` — again the wrong calendar day, and again only east of UTC. A calendar date has no instant to convert, and requiring it leaves the caller as the only party who decides what "today" means.