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.Domain/Common/Exceptions/BadRequestException.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.Serialization;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace DocumentService.Domain.Common.Exceptions;
+
+public class BadRequestException : Exception
+{
+    public BadRequestException()
+    {
+    }
+
+    public BadRequestException(string? message) : base(message)
+    {
+    }
+
+    public BadRequestException(string? message, Exception? innerException) : base(message, innerException)
+    {
+    }
+}

DocumentService.Domain/Common/Exceptions/DomainException.cs

@@ -0,0 +1,26 @@
+namespace DocumentService.Domain.Common.Exceptions;
+
+/// <summary>
+/// Base exception for all domain-related exceptions.
+/// Caught by the Exception Handling Middleware in the API layer.
+/// </summary>
+[Obsolete("This exception is deprecated. Use more specific exceptions for domain errors.")]
+public abstract class DomainException : Exception
+{
+    /// <summary>
+    /// Error code for categorization and logging.
+    /// </summary>
+    public string ErrorCode { get; }
+
+    protected DomainException(string message, string errorCode) 
+        : base(message)
+    {
+        ErrorCode = errorCode;
+    }
+
+    protected DomainException(string message, string errorCode, Exception innerException) 
+        : base(message, innerException)
+    {
+        ErrorCode = errorCode;
+    }
+}

DocumentService.Domain/Common/Exceptions/DomainValidationException.cs

@@ -0,0 +1,29 @@
+namespace DocumentService.Domain.Common.Exceptions;
+
+/// <summary>
+/// Exception thrown when domain validation fails (e.g., invalid Value Objects).
+/// Maps to HTTP 400 Bad Request in the API layer.
+/// </summary>
+[Obsolete("This exception is deprecated. Use more specific exceptions for domain validation errors.")]
+public class DomainValidationException : DomainException
+{
+    public string PropertyName { get; }
+
+    public DomainValidationException(string message)
+        : base(message, "DOMAIN_VALIDATION_ERROR")
+    {
+        PropertyName = string.Empty;
+    }
+
+    public DomainValidationException(string propertyName, string message)
+        : base(message, "DOMAIN_VALIDATION_ERROR")
+    {
+        PropertyName = propertyName;
+    }
+
+    public DomainValidationException(string message, Exception innerException)
+        : base(message, "DOMAIN_VALIDATION_ERROR", innerException)
+    {
+        PropertyName = string.Empty;
+    }
+}

DocumentService.Domain/Common/Exceptions/NotFoundException.cs

@@ -0,0 +1,22 @@
+using System.Runtime.Serialization;
+
+namespace DocumentService.Domain.Common.Exceptions;
+
+/// <summary>
+/// Exception thrown when a requested resource is not found.
+/// Maps to HTTP 404 Not Found in the API layer.
+/// </summary>
+public class NotFoundException : Exception
+{
+    public NotFoundException()
+    {
+    }
+
+    public NotFoundException(string? message) : base(message)
+    {
+    }
+
+    public NotFoundException(string? message, Exception? innerException) : base(message, innerException)
+    {
+    }
+}