Send puzzle-solved notifications only to the solved-puzzle's hunt

[zarvox]

Fix an unindexed Puzzles find query that also probably wants to limit to the current hunt while I'm here.

Fixes #1991.

[ebroder]

LGTM. Are you sure that there's not also a bug with tagging a puzzle from the wrong hunt?

[zarvox]

Yes, the logic here is sufficient to explain the observed behavior (we happened to have at least two group:runaround tags in the DB, and the puzzle we saw the notification for was meta-for:runaround, and we didn't have a hunt selector on this query). I checked all the places we fetch tags in the client components, and these are the only ones that didn't specify either an _id or a hunt.