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>

db/queries.sql

@@ -69,6 +69,9 @@ DELETE FROM rsvps WHERE id = ?;
 -- name: CountRsvps :one
 SELECT COUNT(*) FROM rsvps WHERE event_id = ?;
 
+-- name: GetRsvpByName :one
+SELECT * FROM rsvps WHERE event_id = ? AND name = ? COLLATE NOCASE LIMIT 1;
+
 -- name: GetUserByPhone :one
 SELECT * FROM users WHERE phone = ?;