fix: waitlist handler handles int id, add alter migration for existing waitlist table

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

go-backend/internal/handlers/admin_handler.go

@@ -4443,12 +4443,13 @@ func (h *AdminHandler) AdminListWaitlist(c *gin.Context) {
 
 	var entries []gin.H
 	for rows.Next() {
-		var id, email string
+		var id any // int or uuid depending on schema
+		var email string
 		var name, referralCode, invitedBy, wlStatus, notes *string
 		var createdAt, updatedAt time.Time
 		if err := rows.Scan(&id, &email, &name, &referralCode, &invitedBy, &wlStatus, &notes, &createdAt, &updatedAt); err == nil {
 			entries = append(entries, gin.H{
-				"id": id, "email": email, "name": name,
+				"id": fmt.Sprintf("%v", id), "email": email, "name": name,
 				"referral_code": referralCode, "invited_by": invitedBy,
 				"status": wlStatus, "notes": notes,
 				"created_at": createdAt, "updated_at": updatedAt,

go-backend/migrations/20260218_waitlist_alter.sql

@@ -0,0 +1,12 @@
+-- Alter existing waitlist table to add missing columns
+
+ALTER TABLE waitlist
+  ADD COLUMN IF NOT EXISTS referral_code text,
+  ADD COLUMN IF NOT EXISTS invited_by    text,
+  ADD COLUMN IF NOT EXISTS status        text NOT NULL DEFAULT 'pending',
+  ADD COLUMN IF NOT EXISTS notes         text,
+  ADD COLUMN IF NOT EXISTS name          text,
+  ADD COLUMN IF NOT EXISTS updated_at    timestamptz NOT NULL DEFAULT now();
+
+CREATE INDEX IF NOT EXISTS idx_waitlist_status ON waitlist(status);
+CREATE INDEX IF NOT EXISTS idx_waitlist_created ON waitlist(created_at DESC);