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