Rebrand project: DocumentOperator to DocumentService

This commit implements a complete rebranding of the project:
- Updated all namespaces from `DocumentOperator` to `DocumentService`.
- Renamed file paths, embedded resources, and test data references.
- Updated configuration keys, logging paths, and Redis instance names.
- Revised documentation to reflect the new project name.
- Modified project and solution files to align with the new structure.
- Updated class names, DTOs, commands, queries, and handlers.
- Adjusted middleware, controllers, and API endpoints.
- Updated Swagger metadata and API titles to `DocumentService API`.
- Refactored test namespaces, resource paths, and embedded resources.
- Updated build and deployment configurations for the new name.
- Replaced all references to `DocumentOperator` in comments and literals.

These changes ensure consistency across the codebase and documentation.

DocumentOperator.API/Controllers/ZugferdController.cs

@@ -1,12 +1,12 @@
-using DocumentOperator.Application.Common.DTOs;
-using DocumentOperator.Application.ExtractZugferd;
-using DocumentOperator.Application.HasZugferd.Queries;
-using DocumentOperator.Domain.Common.Exceptions;
+using DocumentService.Application.Common.DTOs;
+using DocumentService.Application.ExtractZugferd;
+using DocumentService.Application.HasZugferd.Queries;
+using DocumentService.Domain.Common.Exceptions;
 using MediatR;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 
-namespace DocumentOperator.API.Controllers;
+namespace DocumentService.API.Controllers;
 
 /// <summary>
 /// Controller for ZUGFeRD operations (detection, extraction)