Apply code review suggestions: use String.Equals for status comparison and filter deleted discounts

Co-authored-by: niemyjski <1020579+niemyjski@users.noreply.github.com>

Author: Copilot

src/Exceptionless.Web/Controllers/OrganizationController.cs

@@ -239,7 +239,7 @@ public async Task<ActionResult<Invoice>> GetInvoiceAsync(string id)
             OrganizationId = organization.Id,
             OrganizationName = organization.Name,
             Date = stripeInvoice.Created,
-            Paid = stripeInvoice.Status == "paid",
+            Paid = String.Equals(stripeInvoice.Status, "paid"),
             Total = stripeInvoice.Total / 100.0m
         };
 
@@ -260,7 +260,7 @@ public async Task<ActionResult<Invoice>> GetInvoiceAsync(string id)
             invoice.Items.Add(item);
         }
 
-        var coupon = stripeInvoice.Discounts?.FirstOrDefault()?.Coupon;
+        var coupon = stripeInvoice.Discounts?.FirstOrDefault(d => d.Deleted is false)?.Coupon;
         if (coupon is not null)
         {
             if (coupon.AmountOff.HasValue)