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.Infrastructure/DependencyInjection.cs

@@ -0,0 +1,26 @@
+using DocumentService.Application.Common.Interfaces;
+using DocumentService.Infrastructure.Services.PdfProcessing;
+using DocumentService.Infrastructure.Services.QrCodeProcessing;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DocumentService.Infrastructure;
+
+/// <summary>
+/// Dependency Injection configuration for Infrastructure Layer
+/// </summary>
+public static class DependencyInjection
+{
+    /// <summary>
+    /// Registers Infrastructure Layer services (DevExpress, File Storage, etc.)
+    /// </summary>
+    public static IServiceCollection AddInfrastructure(this IServiceCollection services)
+    {
+        // PDF Processing Service (DevExpress)
+        services.AddScoped<IPdfProcessor, DevExpressPdfProcessor>();
+
+        // Swiss QR Code Processing Service (DevExpress + Codecrete + ZXing)
+        services.AddScoped<ISwissQrCodeProcessor, DevExpressSwissQrCodeProcessor>();
+
+        return services;
+    }
+}