feat(user): add createdAt field to user model

- Add createdAt field to User struct and database schema
- Update all user queries to include createdAt field
- Document new field in API documentation
- Fix server online status flag timing

main.go

@@ -89,10 +89,10 @@ func main() {
 
 	go func() {
 		postLog.Info(fmt.Sprintf("Server starting on %s", addr))
+		isOnline = true
 		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
 			postLog.Fatal(fmt.Sprintf("Failed to start server: %v", err))
 		}
-		isOnline = true
 	}()
 
 	go func() {