Refactor: Rename DocumentOperator to DocumentService

Updated project and solution files to rename and restructure
`DocumentOperator` to `DocumentService`. Modified project
references in `DocumentService.API.csproj`, `DocumentService.Application.csproj`,
and `DocumentService.Infrastructure.csproj` to reflect the new
naming convention. Updated `DocumentService.sln` to remove
old project references, add new ones, and adjust configuration
and nested project mappings accordingly. This change aligns
the project structure with the new naming convention.

DocumentService.Application/CheckPdfAttachments/Queries/CheckPdfAttachmentsQuery.cs

@@ -0,0 +1,37 @@
+using AutoMapper;
+using DocumentService.Application.Common.DTOs;
+using DocumentService.Application.Common.Interfaces;
+using MediatR;
+
+namespace DocumentService.Application.CheckPdfAttachments.Queries;
+
+/// <summary>
+/// Query for checking PDF attachments (Stream-based)
+/// </summary>
+public record CheckPdfAttachmentsQuery : IRequest<AttachmentCheckResult>
+{
+    /// <summary>
+    /// PDF as stream (caller is responsible for disposal)
+    /// </summary>
+    public required Stream PdfStream { get; init; }
+}
+
+/// <summary>
+/// Handler for CheckPdfAttachmentsQuery
+/// Orchestrates PDF attachment checking using IPdfProcessor and AutoMapper
+/// </summary>
+public class CheckPdfAttachmentsQueryHandler(IPdfProcessor PdfProcessor, IMapper Mapper)
+    : IRequestHandler<CheckPdfAttachmentsQuery, AttachmentCheckResult>
+{
+    /// <summary>
+    /// Checks PDF attachments and returns detailed metadata
+    /// </summary>
+    public async Task<AttachmentCheckResult> Handle(CheckPdfAttachmentsQuery request, CancellationToken cancellationToken)
+    {
+        // Call DevExpress service directly with stream (exceptions propagate naturally)
+        var attachmentInfo = await PdfProcessor.CheckAttachmentsAsync(request.PdfStream);
+
+        // Map DTO to response DTO using AutoMapper
+        return Mapper.Map<AttachmentCheckResult>(attachmentInfo);
+    }
+}