Redirect emails to dev address in non-production; fix PAID stamp color

- EmailService: add RedirectIfNonProd() mirroring SmsService pattern;
  reads SendGrid:DevRedirectEmail and redirects all outbound email in
  non-production so real customers are never contacted on local/dev
- appsettings.json: set DevRedirectEmail to spouliot@scppowdercoating.com
- PdfService: revert Opacity() (not in QuestPDF 2024.12.3); use
  Colors.Green.Lighten2 for stamp + border to achieve lighter look

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Application/Services/PdfService.cs

@@ -175,16 +175,15 @@ public class PdfService : IPdfService
         container
             .AlignCenter()
             .AlignMiddle()
-            .Opacity(0.35f)
             .Rotate(-45f)
-            .Border(3)
-            .BorderColor(Colors.Green.Darken2)
+            .Border(2)
+            .BorderColor(Colors.Green.Lighten2)
             .PaddingVertical(10)
             .PaddingHorizontal(20)
             .Text("PAID")
             .FontSize(52)
             .Bold()
-            .FontColor(Colors.Green.Darken2);
+            .FontColor(Colors.Green.Lighten2);
     }
 
     /// <summary>