feat: add NATS.Server.Host console app with basic CLI arguments

src/NATS.Server.Host/Program.cs

@@ -1,2 +1,40 @@
-// See https://aka.ms/new-console-template for more information
-Console.WriteLine("Hello, World!");
+// src/NATS.Server.Host/Program.cs
+using NATS.Server;
+
+var options = new NatsOptions();
+
+// Simple CLI argument parsing
+for (int i = 0; i < args.Length; i++)
+{
+    switch (args[i])
+    {
+        case "-p" or "--port" when i + 1 < args.Length:
+            options.Port = int.Parse(args[++i]);
+            break;
+        case "-a" or "--addr" when i + 1 < args.Length:
+            options.Host = args[++i];
+            break;
+        case "-n" or "--name" when i + 1 < args.Length:
+            options.ServerName = args[++i];
+            break;
+    }
+}
+
+var server = new NatsServer(options);
+
+var cts = new CancellationTokenSource();
+Console.CancelKeyPress += (_, e) =>
+{
+    e.Cancel = true;
+    cts.Cancel();
+};
+
+Console.WriteLine($"[NATS] Listening on {options.Host}:{options.Port}");
+
+try
+{
+    await server.StartAsync(cts.Token);
+}
+catch (OperationCanceledException) { }
+
+Console.WriteLine("[NATS] Server stopped.");