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>

main.go

@@ -134,6 +134,10 @@ func main() {
 	pageTmpl["slots"] = template.Must(
 		template.New("").Funcs(funcMap).ParseFS(templateFS, "templates/slots.html"),
 	)
+	// edit-rsvp modal partial
+	pageTmpl["edit-rsvp"] = template.Must(
+		template.New("").Funcs(funcMap).ParseFS(templateFS, "templates/edit-rsvp.html"),
+	)
 
 	srv := NewServer(database, baseURL, features)
 
@@ -175,9 +179,10 @@ func main() {
 	// Guest event view
 	r.Get("/e/{slug}", srv.handleEvent)
 	r.Get("/e/{slug}/slots", srv.handleSlotsPartial)
-	r.Post("/e/{slug}/claim", srv.handleClaim)
-	r.Delete("/e/{slug}/claim/{claimID}", srv.handleUnclaim)
 	r.Post("/e/{slug}/rsvp", srv.handleRsvp)
+	r.Delete("/e/{slug}/claim/{claimID}", srv.handleUnclaim)
+	r.Get("/e/{slug}/rsvp/{rsvpID}/edit", srv.handleEditRsvpForm)
+	r.Put("/e/{slug}/rsvp/{rsvpID}", srv.handleUpdateRsvp)
 	r.Delete("/e/{slug}/rsvp/{rsvpID}", srv.handleUnrsvp)
 
 	// OG image