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/Common/Behaviors/LoggingBehavior.cs

@@ -0,0 +1,56 @@
+using MediatR;
+using Microsoft.Extensions.Logging;
+using System.Diagnostics;
+
+namespace DocumentService.Application.Common.Behaviors;
+
+/// <summary>
+/// MediatR Pipeline Behavior that logs requests and tracks performance
+/// Executes AFTER ValidationBehavior, BEFORE Handler
+/// </summary>
+public class LoggingBehavior<TRequest, TResponse>(ILogger<LoggingBehavior<TRequest, TResponse>> Logger) : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : IRequest<TResponse>
+{
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+    {
+        var requestName = typeof(TRequest).Name;
+
+        // Performance Tracking
+        var stopwatch = Stopwatch.StartNew();
+
+        try
+        {
+            // Handler ausführen
+            var response = await next(cancellationToken);
+
+            stopwatch.Stop();
+
+            // Request Success
+            Logger.LogInformation(
+                "Handled {RequestName} in {ElapsedMs}ms",
+                requestName,
+                stopwatch.ElapsedMilliseconds
+            );
+
+            return response;
+        }
+        catch (Exception ex)
+        {
+            stopwatch.Stop();
+
+            // Request Failed
+            Logger.LogError(
+                ex,
+                "Error handling {RequestName} after {ElapsedMs}ms: {ErrorMessage}",
+                requestName,
+                stopwatch.ElapsedMilliseconds,
+                ex.Message
+            );
+
+            throw; // Exception weiterwerfen (wird von Exception Middleware gefangen)
+        }
+    }
+}