Auto-RSVP when claiming a slot

Claiming a slot now also adds the person to the going list if they
aren't already there (case-insensitive name match).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

handlers.go

@@ -310,6 +310,16 @@ func (s *Server) handleClaim(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Auto-RSVP if they're not already on the going list
+	_, err = s.q.GetRsvpByName(r.Context(), db.GetRsvpByNameParams{
+		EventID: event.ID, Name: name,
+	})
+	if err == sql.ErrNoRows {
+		s.q.CreateRsvp(r.Context(), db.CreateRsvpParams{
+			EventID: event.ID, Name: name,
+		})
+	}
+
 	s.notify(slug)
 
 	// Return updated slots partial