Add edit RSVP modal, plus-one tracking, and unified signup form

Merge RSVP + slot claim into a single form. Add plus_one field to RSVPs.
Add clickable RSVP names that open a modal to edit name/note/plus_one.

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

db/queries.sql

@@ -59,8 +59,8 @@ SELECT COUNT(*) FROM claims WHERE slot_id = ?;
 SELECT * FROM rsvps WHERE event_id = ? ORDER BY created_at;
 
 -- name: CreateRsvp :one
-INSERT INTO rsvps (event_id, name, note)
-VALUES (?, ?, ?)
+INSERT INTO rsvps (event_id, name, note, plus_one)
+VALUES (?, ?, ?, ?)
 RETURNING *;
 
 -- name: DeleteRsvp :exec
@@ -120,3 +120,9 @@ SELECT * FROM events WHERE user_id = ? ORDER BY created_at DESC;
 
 -- name: SetEventUser :exec
 UPDATE events SET user_id = ? WHERE id = ?;
+
+-- name: GetRsvp :one
+SELECT * FROM rsvps WHERE id = ?;
+
+-- name: UpdateRsvp :exec
+UPDATE rsvps SET name = ?, note = ?, plus_one = ? WHERE id = ?;