Restore all zeroed views + add bulk gift certificate creation

The HTML entity sweep script had a bug where it wrote empty files for any
view that contained no target Unicode characters, zeroing out 215 view files.
All views restored from the pre-sweep commit (cefdf3e).

Bulk gift certificate feature:
- BulkCreateGiftCertificateDto with Quantity (1-500), Amount, Reason, Expiry, Notes
- GenerateBulkGiftCertificatePdfAsync on IPdfService / PdfService: one Letter page
  per cert, reusing the same purple/gold branded ComposeGiftCertificateContent helper
- GiftCertificatesController: BulkCreate GET/POST, BulkResult GET, BulkDownloadPdf POST
- Views: BulkCreate.cshtml (form with live total preview), BulkResult.cshtml (table +
  Download All PDF button that POSTs cert IDs to avoid URL length limits)
- gift-certificate-bulk.js: live preview + spinner/disable on submit
- Index.cshtml: Bulk Create button added alongside New Certificate

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

src/PowderCoating.Web/Views/Payment/Success.cshtml

@@ -0,0 +1,20 @@
+@{
+    Layout = "~/Views/Shared/_QuoteApprovalLayout.cshtml";
+    ViewData["Title"] = "Payment Successful";
+    ViewBag.CompanyName = "";
+}
+
+<div class="container py-5" style="max-width:480px;">
+    <div class="card p-4 text-center">
+        <i class="bi bi-check-circle-fill text-success" style="font-size:3.5rem;"></i>
+        <h4 class="mt-3 fw-bold">Payment Received!</h4>
+        <p class="text-muted mb-0">
+            Thank you — your payment has been processed successfully.
+            You'll receive a confirmation once your payment is verified by the shop.
+        </p>
+        <hr class="my-3" />
+        <p class="text-muted small mb-0">
+            If you have questions, please contact the shop directly.
+        </p>
+    </div>
+</div>