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/PHASENPLAN.md

@@ -1,4 +1,4 @@
-# ?? DocumentOperator - Phasenplan (Feature-Driven Development)
+# ?? DocumentService - Phasenplan (Feature-Driven Development)
 
 > **Stand:** 17.01.2025 | **Aktuell:** Feature 3 - ExtractAttachments ? NEXT | **Projektdauer:** 6 Wochen
 
@@ -132,7 +132,7 @@
    - ? XML Comments aktiviert
 
 2. **XML-Dokumentation aktiviert**
-   - ? `API/DocumentOperator.API.csproj`
+   - ? `API/DocumentService.API.csproj`
    - ? `<GenerateDocumentationFile>true</GenerateDocumentationFile>`
 
 3. **Endpoint Dokumentation**
@@ -146,12 +146,12 @@
 
 5. **Program.cs Updates**
    - ? `builder.Services.AddSwaggerDocumentation()` statt `AddSwaggerGen()`
-   - ? `using DocumentOperator.API.Configuration;` hinzugefügt
+   - ? `using DocumentService.API.Configuration;` hinzugefügt
 
 **Akzeptanzkriterien:**
 - ? Build erfolgreich
 - ? Alle Tests grün (11/11)
-- ? XML-Dokumentation wird generiert (`DocumentOperator.API.xml`)
+- ? XML-Dokumentation wird generiert (`DocumentService.API.xml`)
 - ? Swagger UI zeigt Endpoint `/api/v1/documents/validate` mit Dokumentation
 - ? Request/Response-Schemas sind dokumentiert
 - ? Endpoint ist im Swagger UI testbar