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.Application/DTOs/GiftCertificate/GiftCertificateDtos.cs

@@ -87,3 +87,27 @@ public class RedeemGiftCertificateDto
     [Range(0.01, 9999.99)]
     public decimal Amount { get; set; }
 }
+
+public class BulkCreateGiftCertificateDto
+{
+    [Required]
+    [Range(1, 500, ErrorMessage = "Quantity must be between 1 and 500.")]
+    [Display(Name = "Number of Certificates")]
+    public int Quantity { get; set; } = 25;
+
+    [Required]
+    [Range(1.00, 9999.99, ErrorMessage = "Amount must be between $1.00 and $9,999.99.")]
+    [Display(Name = "Face Value (each)")]
+    public decimal Amount { get; set; }
+
+    [Required]
+    [Display(Name = "Issued Reason")]
+    public GiftCertificateIssuedReason IssuedReason { get; set; } = GiftCertificateIssuedReason.Promotional;
+
+    [Display(Name = "Expiry Date (optional)")]
+    public DateTime? ExpiryDate { get; set; }
+
+    [StringLength(1000)]
+    [Display(Name = "Event / Notes (applied to all certificates)")]
+    public string? Notes { get; set; }
+}