test(nuget): add NuGet smoke-test console app (DocumentService.Tests.NuGet)

Standalone console application that references the published DocumentService.Client
NuGet package (v1.2.2) and verifies the full happy-path against a live API instance.

- Targets net8.0; references DocumentService.Client 1.2.2 via NuGet (not project ref)
- Embeds valid.pdf as an EmbeddedResource so no file-system path is required
- Calls Client.Validation.ValidateAsync(Stream) and prints PageCount, PdfVersion,
  IsEncrypted, AttachmentCount, FileSizeBytes to stdout
- Handles HttpRequestException and InvalidOperationException with descriptive output
- Intended to run once after a new package is pushed to confirm the .nupkg bundles
  Application and Domain DLLs correctly (validates the embedding targets added in
  the previous commit)

DocumentService.Tests.NuGet/Program.cs

@@ -0,0 +1,36 @@
+using DocumentService.Client;
+
+// 1. Configure the client
+Client.Configure("http://172.24.12.39:9393/");
+
+// 2. Load embedded PDF resource
+var assembly = typeof(Program).Assembly;
+var resourceName = assembly.GetManifestResourceNames()
+    .FirstOrDefault(n => n.EndsWith("valid.pdf", StringComparison.OrdinalIgnoreCase));
+
+if (resourceName is null)
+{
+    Console.WriteLine("❌ Embedded resource 'valid.pdf' not found.");
+    return;
+}
+
+try
+{
+    using var stream = assembly.GetManifestResourceStream(resourceName)!;
+    var result = await Client.Validation.ValidateAsync(stream);
+
+    Console.WriteLine("✅ Connection successful!");
+    Console.WriteLine($"   Page count   : {result.PageCount}");
+    Console.WriteLine($"   PDF version  : {result.PdfVersion}");
+    Console.WriteLine($"   Encrypted    : {result.IsEncrypted}");
+    Console.WriteLine($"   Attachments  : {result.AttachmentCount}");
+    Console.WriteLine($"   File size    : {result.FileSizeMB:F2} MB");
+}
+catch (HttpRequestException ex)
+{
+    Console.WriteLine("❌ HTTP error: " + ex.Message);
+}
+catch (InvalidOperationException ex)
+{
+    Console.WriteLine("❌ Client error: " + ex.Message);
+}