RSVP improvements

Wasn’t this feature recently added, @AndrewL?

https://discussions.scouting.org/t/june-3-2025-scoutbook-plus-updates/491969

It’s possible that it’s not as straightforward when there are multiple individuals represented, though. I don’t have any youth left in my unit, so I’m not sure what the interface looks like for a parent/scouter or parent of multiple scouts in one unit.