Add IMAP support for email fetching and marking as seen

Introduced IMAP functionality to enable fetching emails from an
IMAP server and marking messages as seen. Updated the
`EmailAccountDto` class with IMAP-related properties
(`ImapServer`, `ImapPort`, `ImapUseSsl`) for configuration.

Added `ReceivedEmailContext` to represent received emails and
created the `IImapEmailService` interface with methods
`FetchEmailsAsync` and `MarkAsSeenAsync`. Implemented the
`LimilabsImapEmailService` class using Limilabs Mail.dll for
IMAP operations, including connection handling, email fetching,
and marking messages as seen.

Added `FetchEmailsQuery` and `MarkEmailAsSeenCommand` with
handlers to encapsulate IMAP logic. Updated `EmailsController`
with new endpoints for fetching emails and marking messages as
seen. Registered `IImapEmailService` in `DependencyInjection`.

Included exception handling and logging for robust error
management during IMAP operations.

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

@@ -1,4 +1,7 @@
 using DigitalData.MessagingService.Application.EmailSending.Commands;
+using DigitalData.MessagingService.Application.EmailReceiving.Queries;
+using DigitalData.MessagingService.Application.EmailReceiving.Commands;
+using DigitalData.MessagingService.Application.EmailAccount.Queries;
 using DigitalData.MessagingService.Abstraction;
 using MediatR;
 using Microsoft.AspNetCore.Mvc;
@@ -13,6 +16,7 @@ namespace DigitalData.MessagingService.API.Controllers;
 [Route("api/[controller]")]
 public class EmailsController(IMediator mediator) : ControllerBase
 {
+    #region Send
     /// <summary>
     /// Send an email, optionally with file attachments.
     /// Omit the <c>attachments</c> field for a plain send.
@@ -61,4 +65,68 @@ public class EmailsController(IMediator mediator) : ControllerBase
 
         return result;
     }
+    #endregion Send
+
+    #region Receive
+    /// <summary>
+    /// Fetch emails from an IMAP mailbox.
+    /// </summary>
+    /// <param name="accountId">Id of the email account (must have ImapServer configured).</param>
+    /// <param name="folder">Mailbox folder to read (default: INBOX).</param>
+    /// <param name="unseenOnly">Return only unread messages.</param>
+    /// <param name="maxCount">Maximum number of messages to return (most-recent first, default: 50).</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>HTTP 200 with list of received emails.</returns>
+    [HttpGet]
+    [ProducesResponseType(StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> FetchEmails(
+        [FromQuery] int accountId,
+        [FromQuery] string folder = "INBOX",
+        [FromQuery] bool unseenOnly = false,
+        [FromQuery] int maxCount = 50,
+        CancellationToken cancellationToken = default)
+    {
+        var query = new FetchEmailsQuery
+        {
+            Account = new GetSenderQuery { Id = accountId },
+            Folder = folder,
+            UnseenOnly = unseenOnly,
+            MaxCount = maxCount
+        };
+
+        var emails = await mediator.Send(query, cancellationToken);
+        return Ok(emails);
+    }
+
+    /// <summary>
+    /// Mark a single IMAP message as seen (read).
+    /// </summary>
+    /// <param name="accountId">Id of the email account.</param>
+    /// <param name="uid">UID of the message on the IMAP server.</param>
+    /// <param name="folder">Mailbox folder the message resides in (default: INBOX).</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>HTTP 204 No Content.</returns>
+    [HttpPatch("{uid}/seen")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> MarkAsSeen(
+        [FromRoute] long uid,
+        [FromQuery] int accountId,
+        [FromQuery] string folder = "INBOX",
+        CancellationToken cancellationToken = default)
+    {
+        var command = new MarkEmailAsSeenCommand
+        {
+            Account = new GetSenderQuery { Id = accountId },
+            Uid = uid,
+            Folder = folder
+        };
+
+        await mediator.Send(command, cancellationToken);
+        return NoContent();
+    }
+    #endregion Receive
 }