refactor: modularize email processing logic and improve service structure

- Extract email template handling, rendering, and sending code into `Worker.Services` project.
- Introduce `EmailTemplateService`, `EmailTemplateRenderingService`, and `SendEmailService`.
- Simplify consumer logic by delegating to scoped services.
- Update project dependencies and package references accordingly.

HrynCo.NotificationService.Services/EmailChannels/Send/SendEmailHandler.cs

@@ -1,5 +1,6 @@
 using System.Net;
 using System.Net.Mail;
+using System.Text;
 using HrynCo.NotificationService.DAL.Abstract.Providers;
 using HrynCo.NotificationService.DAL.Abstract.Repositories;
 using HrynCo.NotificationService.Services.Core;
@@ -48,14 +49,16 @@ internal sealed class SendEmailHandler
             {
                 From = new MailAddress(smtp.FromEmail, smtp.FromName),
                 Subject = request.Subject,
-                Body = request.HtmlBody,
-                IsBodyHtml = true
+                Body = request.TextBody ?? string.Empty,
+                IsBodyHtml = false,
+                BodyEncoding = Encoding.UTF8,
+                SubjectEncoding = Encoding.UTF8
             };
 
-            if (!string.IsNullOrWhiteSpace(request.TextBody))
+            if (!string.IsNullOrWhiteSpace(request.HtmlBody))
             {
-                var plain = AlternateView.CreateAlternateViewFromString(request.TextBody, null, "text/plain");
-                mail.AlternateViews.Add(plain);
+                var html = AlternateView.CreateAlternateViewFromString(request.HtmlBody, Encoding.UTF8, "text/html");
+                mail.AlternateViews.Add(html);
             }
 
             mail.To.Add(new MailAddress(request.RecipientEmail, request.RecipientName));