feat(ui): add RSVP attendance option and admin features

* Implement attendance selection in RSVP form
* Add admin endpoints for managing RSVPs and guests
* Update RSVP handling to include attendance status

server/internal/mail/mail.go

@@ -93,7 +93,11 @@ func (m *Mailer) SendRSVP(r store.RSVP, allGuests []store.Guest) error {
 	joined := strings.Join(names, ", ")
 
 	var b strings.Builder
-	fmt.Fprintf(&b, "New RSVP for %d guest(s) — %d adult(s), %d child(ren): %s\n", len(r.Guests), adults, children, joined)
+	if r.Attending {
+		fmt.Fprintf(&b, "New RSVP (ATTENDING) for %d guest(s) — %d adult(s), %d child(ren): %s\n", len(r.Guests), adults, children, joined)
+	} else {
+		fmt.Fprintf(&b, "New RSVP (NOT ATTENDING) — %s\n", joined)
+	}
 	if r.Message != "" {
 		fmt.Fprintf(&b, "\nMessage:\n%s\n", r.Message)
 	}
@@ -113,7 +117,11 @@ func (m *Mailer) SendRSVP(r store.RSVP, allGuests []store.Guest) error {
 		fmt.Fprintf(&b, "\n%d adult(s), %d child(ren) total\n", totalAdults, totalChildren)
 	}
 
-	return m.send(fmt.Sprintf("RSVP from %s", joined), m.header("an RSVP is made")+b.String())
+	subjectState := "attending"
+	if !r.Attending {
+		subjectState = "not attending"
+	}
+	return m.send(fmt.Sprintf("RSVP from %s (%s)", joined, subjectState), m.header("an RSVP is made")+b.String())
 }
 
 func (m *Mailer) SendPhotoUpload(u store.PhotoUpload, files []store.PhotoFile) error {