fix: Register CodePagesEncodingProvider for Limilabs Mail.dll compatibility

- Add static constructor to register System.Text.Encoding.CodePages
- Required for windows-1252 and other extended code page support
- Fixes encoding issues with international email content

src/DigitalData.EmailProfiler.Infrastructure/Services/LimilabsEmailService.cs

@@ -1,3 +1,4 @@
+using System.Text;
 using DigitalData.EmailProfiler.Application.Common.Dtos;
 using DigitalData.EmailProfiler.Application.Common.Interfaces;
 using DigitalData.EmailProfiler.Domain.Exceptions;
@@ -19,6 +20,12 @@ public class LimilabsEmailService(
 {
     private readonly EmailAccountDto _smtpAccount = smtpConfig.Value;
 
+    // Register encoding provider for Limilabs (requires windows-1252 and other code pages)
+    static LimilabsEmailService()
+    {
+        Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
+    }
+
     public async Task SendEmailAsync(string to, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default)
     {
         using var smtp = new Smtp();