feat(test): add mock PVE API server for integration testing

ASP.NET Minimal API project that simulates the Proxmox VE API using
existing JSON fixtures. Supports ticket and API token auth, request
tracking for assertions, self-signed HTTPS, and all major API endpoints.
Designed for programmatic test startup via MockPveServer.Start().

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/PSProxmoxVE.MockServer/Program.cs

@@ -0,0 +1,22 @@
+using PSProxmoxVE.MockServer;
+
+// When run standalone, start on a fixed port
+using var server = MockPveServer.Start(port: 8006);
+Console.WriteLine($"Mock Proxmox VE API server running at {server.BaseUrl}");
+Console.WriteLine("Press Ctrl+C to stop.");
+
+var cts = new CancellationTokenSource();
+Console.CancelKeyPress += (_, e) =>
+{
+    e.Cancel = true;
+    cts.Cancel();
+};
+
+try
+{
+    await Task.Delay(Timeout.Infinite, cts.Token);
+}
+catch (OperationCanceledException)
+{
+    // Graceful shutdown
+}