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/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -23,8 +23,11 @@ public static class DependencyInjection
         IConfiguration configuration)
     {
         // --- External Services ---
-        // Email Service (using Limilabs Mail.dll - Singleton for use in EmailSenderWorker)
+        // Email Service - SMTP outbound (Limilabs Mail.dll)
         services.AddSingleton<IEmailService, LimilabsEmailService>();
+
+        // Email Service - IMAP inbound (Limilabs Mail.dll)
+        services.AddSingleton<IImapEmailService, LimilabsImapEmailService>();
         
         // PDF Processing Service (using DevExpress.Pdf)
         services.AddScoped<IPdfProcessingService, DevExpressPdfProcessingService>();