Returns the raw quota row for (computeNodeId, userId), or 404 if none
is set for that pair. A 404 does NOT mean "no limit applies" — the
user still falls back to the node __default__ row, then to a
platform safety cap. Use /effective to see what's actually enforced.

Pass __default__ as userId to retrieve the node-wide default
(owner-only).

Pass me as userId to retrieve the caller's own row without
having to know your own user node id.

Permissions: Node owner / workspace admin can read any row; the
caller can also read their own row (userId matches their JWT or
me) provided they have any access to the node.