Add missing XML doc comments to resolve CS1591 warnings:
- SerilogConfiguration: Class comment
- SwaggerConfiguration: Class and AddSwaggerDocumentation() method
- ExceptionHandlingMiddleware: Constructor and InvokeAsync() method
- RequestLoggingMiddleware: Placeholder class comment
- TenantResolutionMiddleware: Placeholder class comment
- Program: Partial class comment for integration test access
Result: 0 CS1591 warnings in DocumentOperator.API project
Restructured project files across all layers:
- Removed `Controllers` folder reference from `DocumentOperator.API.csproj`.
- Added folder structure to `DocumentOperator.Application`, `DocumentOperator.Domain`, and `DocumentOperator.Infrastructure` projects for better organization.
Introduced new API configurations and middleware:
- Added `SerilogConfiguration` and `SwaggerConfiguration` classes.
- Added `ExceptionHandlingMiddleware`, `RequestLoggingMiddleware`, and `TenantResolutionMiddleware`.
Implemented new document processing feature:
- Added `ProcessDocumentCommand`, `ProcessDocumentHandler`, and `ProcessDocumentValidator` classes in the application layer.
