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.API/Endpoints/v1/DocumentEndpoints.cs

@@ -1,6 +1,67 @@
-namespace DocumentOperator.API.Endpoints.v1
+using DocumentOperator.Application.Common.DTOs;
+using DocumentOperator.Application.Features.Documents.ValidatePdf;
+using DocumentOperator.Domain.Models.ValueObjects;
+using MediatR;
+using Microsoft.AspNetCore.Mvc;
+
+namespace DocumentOperator.API.Endpoints.v1;
+
+/// <summary>
+/// Document endpoints (Minimal API)
+/// </summary>
+public static class DocumentEndpoints
 {
-    public class DocumentEndpoints
+    /// <summary>
+    /// Maps all document-related endpoints
+    /// </summary>
+    public static void MapDocumentEndpoints(this IEndpointRouteBuilder app)
     {
+        var group = app.MapGroup("/api/v1/documents")
+            .WithTags("Documents");
+
+        // POST /api/v1/documents/validate
+        group.MapPost("/validate", ValidatePdf)
+            .WithName("ValidatePdf")
+            .WithSummary("Validates a PDF document and returns metadata")
+            .WithDescription("Validates the PDF format and extracts metadata (page count, file size, PDF version, attachments)")
+            .Produces<ValidatePdfResponse>(StatusCodes.Status200OK)
+            .Produces<ProblemDetails>(StatusCodes.Status400BadRequest)
+            .Produces<ProblemDetails>(StatusCodes.Status500InternalServerError);
+    }
+
+    /// <summary>
+    /// Validates a PDF document and returns metadata
+    /// </summary>
+    /// <param name="request">PDF as Base64 string</param>
+    /// <param name="mediator">MediatR instance</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>PDF metadata (page count, file size, etc.)</returns>
+    /// <response code="200">PDF is valid, metadata returned</response>
+    /// <response code="400">Invalid PDF or Base64 format</response>
+    /// <response code="500">Internal server error during validation</response>
+    private static async Task<IResult> ValidatePdf(
+        ValidatePdfRequest request,
+        IMediator mediator,
+        CancellationToken cancellationToken)
+    {
+        // DTO → Query (Value Objects erstellen - kann DomainValidationException werfen!)
+        var query = new ValidatePdfQuery(
+            Base64String.Create(request.Base64Pdf)
+        );
+
+        // MediatR Handler aufrufen (ValidationBehavior → Handler)
+        var metadata = await mediator.Send(query, cancellationToken);
+
+        // PdfMetadata → Response DTO
+        var response = new ValidatePdfResponse(
+            metadata.PageCount,
+            metadata.FileSizeBytes,
+            metadata.FileSizeMB,
+            metadata.PdfVersion,
+            metadata.HasAttachments,
+            metadata.AttachmentCount
+        );
+
+        return Results.Ok(response);
     }
 }