Add ValidatePDF feature with API, Swagger, and tests

Implemented the ValidatePDF feature end-to-end:
- Added `/api/v1/documents/validate` Minimal API endpoint.
- Introduced centralized ExceptionHandlingMiddleware.
- Configured Swagger with `AddSwaggerDocumentation` extension.
- Enabled XML comments in `DocumentOperator.API.csproj`.
- Updated DTOs with XML comments and added `FileSizeMB`.
- Added integration tests for the ValidatePDF endpoint (3 tests).
- Registered infrastructure services (e.g., `IPdfProcessor`).
- Refactored `Program.cs` to include middleware and endpoints.
- Updated PHASENPLAN.md and ROADMAP.md to reflect progress.
- Cleaned up code and made `Program` accessible for tests.

DocumentOperator.Tests/Integration/API/DocumentEndpointsTests.cs

@@ -0,0 +1,89 @@
+using DocumentOperator.Application.Common.DTOs;
+using FluentAssertions;
+using Microsoft.AspNetCore.Mvc.Testing;
+using System.Net;
+using System.Net.Http.Json;
+using Xunit;
+
+namespace DocumentOperator.Tests.Integration.API;
+
+public class DocumentEndpointsTests : IClassFixture<WebApplicationFactory<Program>>
+{
+    private readonly WebApplicationFactory<Program> _factory;
+    private readonly HttpClient _client;
+
+    public DocumentEndpointsTests(WebApplicationFactory<Program> factory)
+    {
+        _factory = factory;
+        _client = _factory.CreateClient();
+    }
+
+    [Fact]
+    public async Task POST_ValidatePdf_ValidPdf_Returns200()
+    {
+        // Arrange
+        // Verwende ein echtes Test-PDF (embedded resource aus Unit Tests)
+        var assembly = typeof(DocumentEndpointsTests).Assembly;
+        var resourceName = "DocumentOperator.Tests.TestData.Pdfs.valid.pdf";
+
+        byte[] pdfBytes;
+        using (var stream = assembly.GetManifestResourceStream(resourceName))
+        {
+            if (stream == null)
+            {
+                throw new InvalidOperationException($"Test resource '{resourceName}' not found");
+            }
+
+            using var ms = new MemoryStream();
+            await stream.CopyToAsync(ms);
+            pdfBytes = ms.ToArray();
+        }
+
+        var base64Pdf = Convert.ToBase64String(pdfBytes);
+        var request = new ValidatePdfRequest(base64Pdf);
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/v1/documents/validate", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+
+        var result = await response.Content.ReadFromJsonAsync<ValidatePdfResponse>();
+        result.Should().NotBeNull();
+        result!.PageCount.Should().BeGreaterThan(0);
+        result.FileSizeBytes.Should().BeGreaterThan(0);
+        result.PdfVersion.Should().NotBeNullOrEmpty();
+    }
+
+    [Fact]
+    public async Task POST_ValidatePdf_InvalidBase64_Returns400()
+    {
+        // Arrange
+        var request = new ValidatePdfRequest("invalid-base64!!!"); // Kein gültiges Base64
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/v1/documents/validate", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
+
+        var problemDetails = await response.Content.ReadAsStringAsync();
+        problemDetails.Should().Contain("Base64");
+    }
+
+    [Fact]
+    public async Task POST_ValidatePdf_EmptyPdf_Returns400()
+    {
+        // Arrange
+        var request = new ValidatePdfRequest(string.Empty); // Leerer String
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/v1/documents/validate", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
+
+        var problemDetails = await response.Content.ReadAsStringAsync();
+        problemDetails.Should().Contain("cannot be empty");
+    }
+}