Refactor: Replace EmailAttachmentContext with DTO

Replaced `EmailAttachmentContext` with `EmailAttachmentDto` across the codebase to align with the updated DTO naming convention.

- Renamed `EmailAttachmentContext` to `EmailAttachmentDto`.
- Updated property types, method signatures, and return types to use `EmailAttachmentDto`.
- Modified XML documentation references to reflect the new class name.
- Updated `ReceivedEmailContext` to `ReceivedEmailDto` and adjusted related methods and properties.
- Refactored `FetchEmailsAsync` methods and handlers to use `ReceivedEmailDto`.
- Adjusted `BuildAttachmentsAsync` and attachment handling logic in `EmailController` and `LimilabsImapEmailService`.

This refactor ensures consistency and improves code clarity while maintaining functionality.

src/presentation/DigitalData.MessagingService.API/Controllers/EmailController.cs

@@ -56,21 +56,21 @@ public class EmailController(IMediator mediator) : ControllerBase
         return Accepted(new { Id = eventId });
     }
 
-    private static async Task<IEnumerable<EmailAttachmentContext>> BuildAttachmentsAsync(
+    private static async Task<IEnumerable<EmailAttachmentDto>> BuildAttachmentsAsync(
         IFormFileCollection? files,
         CancellationToken cancellationToken)
     {
         if (files is null || files.Count == 0)
             return [];
 
-        var result = new List<EmailAttachmentContext>(files.Count);
+        var result = new List<EmailAttachmentDto>(files.Count);
 
         foreach (var file in files)
         {
             using var ms = new MemoryStream();
             await file.CopyToAsync(ms, cancellationToken);
 
-            result.Add(new EmailAttachmentContext
+            result.Add(new EmailAttachmentDto
             {
                 FileName    = file.FileName,
                 Content     = ms.ToArray(),