Routes an item query through Build*Request() + pool based on queryType. Used for both the main request and the optional 2nd lookup for the # filter. queryType values: "liveTV", "studios", "genres", "artists", "albumArtists", "usersItems"

Fills one genre row with the sampled items its request returned.

res is the pool response AA, or invalid when the request never got an answer — the pool was down, or the whole-run budget expired. An HTTP error arrives as a valid res with ok = false. Both leave the row in place with its title and no children, which is exactly what the blocking fetchJson this replaced did when it returned invalid: a genre that can't be sampled still belongs in the list, and removing it would renumber the grid around a transient failure.