Debug: The Support Queue That Serves VIPs Last

Serve must pop in FIFO order, but the current implementation serves the LAST added ticket first (a Stack is hiding where a Queue belongs). Fix Serve (and only Serve — Add is fine) so tickets leave in arrival order, and Pending stays truthful. ``csharp public class SupportQueue { public void Add(string ticket); public string? Serve(); // null when empty public int Pending { get; } } ``