Refactor IMAP email fetching to use SearchFilter

Replaced individual parameters (`folder`, `unseenOnly`, `maxCount`) in `IImapEmailService` with a consolidated `SearchFilter` object to simplify method signatures and improve maintainability.

Renamed `MailQuery` to `SearchFilter` in `FetchEmailsQuery` for better clarity. Updated `FetchEmailsQueryHandler` and `LimilabsImapEmailService` to use the new `SearchFilter` object, ensuring consistent handling of folder selection, unread message filtering, and message count limits.

Improved logging in `LimilabsImapEmailService` to reflect the updated `SearchFilter` structure.

src/core/DigitalData.MessagingService.Application/Common/Interfaces/IImapEmailService.cs

@@ -11,15 +11,11 @@ public interface IImapEmailService
     /// Fetches emails from the specified mailbox folder.
     /// </summary>
     /// <param name="account">Account whose IMAP settings will be used.</param>
-    /// <param name="folder">Mailbox folder name (e.g. "INBOX"). Defaults to INBOX.</param>
-    /// <param name="unseenOnly">When <see langword="true"/> returns only unread messages.</param>
-    /// <param name="maxCount">Maximum number of messages to retrieve (most-recent first). 0 = unlimited.</param>
+    /// <param name="filter">Filter to apply when fetching emails.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
     Task<IEnumerable<ReceivedEmailContext>> FetchEmailsAsync(
         EmailAccountDto account,
-        string folder = "INBOX",
-        bool unseenOnly = false,
-        int maxCount = 50,
+        FetchEmailsQuery.SearchFilter filter,
         CancellationToken cancellationToken = default);
 
     /// <summary>