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.Infrastructure/Services/EmailService.cs

@@ -47,6 +47,8 @@ public class EmailService : IEmailService
         if (!_hostEnvironment.IsProduction())
             subject = $"[{_hostEnvironment.EnvironmentName}] {subject}";
 
+        (toEmail, toName) = RedirectIfNonProd(toEmail, toName);
+
         var fromEmail = _configuration["SendGrid:FromEmail"] ?? "noreply@example.com";
         var fromName  = _configuration["SendGrid:FromName"]  ?? "Powder Coating";
 
@@ -104,6 +106,8 @@ public class EmailService : IEmailService
         if (!_hostEnvironment.IsProduction())
             subject = $"[{_hostEnvironment.EnvironmentName}] {subject}";
 
+        (toEmail, toName) = RedirectIfNonProd(toEmail, toName);
+
         var fromEmail = _configuration["SendGrid:FromEmail"] ?? "noreply@example.com";
         var fromName  = _configuration["SendGrid:FromName"]  ?? "Powder Coating";
 
@@ -138,6 +142,20 @@ public class EmailService : IEmailService
         }
     }
 
+    /// <summary>
+    /// In non-production environments, redirects outbound email to <c>SendGrid:DevRedirectEmail</c>
+    /// so real customers are never contacted outside of production. Double-gated on environment
+    /// name AND the config value so a misconfigured prod deploy can't accidentally redirect.
+    /// </summary>
+    private (string email, string name) RedirectIfNonProd(string toEmail, string toName)
+    {
+        if (_hostEnvironment.IsProduction()) return (toEmail, toName);
+        var devEmail = _configuration["SendGrid:DevRedirectEmail"];
+        if (string.IsNullOrWhiteSpace(devEmail)) return (toEmail, toName);
+        _logger.LogWarning("Non-production environment: redirecting email from {Original} to dev address {Dev}", toEmail, devEmail);
+        return (devEmail, $"[DEV → {toName} <{toEmail}>]");
+    }
+
     /// <summary>
     /// Sends the built SendGrid message and interprets the HTTP response. Extracted so both
     /// send methods share identical dispatch and logging logic.