Fix invoice re-creation after void; add payment terms selector and shop supplies line

- Voided invoices no longer block creating a new invoice for the same job: voided invoice's
  JobId FK is cleared so the unique index slot is freed for the replacement
- Invoice Details view shows voided invoices as history rather than hiding them
- Payment terms: standardized SelectList (Due on Receipt, Net 15/30/45/60/90, 2% 10 Net 30,
  COD) with custom-term preservation; invoice-due-date.js auto-updates Due Date on term change
- Shop supplies on direct (no-quote) jobs: InvoicesController derives the shop supplies line
  from the company rate when the job has no source quote to read the pre-agreed amount from
- Job entity: ShopSuppliesAmount + ShopSuppliesPercent fields preserved through job lifecycle
- Migration: AddShopSuppliesAmountToJob

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

src/PowderCoating.Application/Mappings/InvoiceProfile.cs

@@ -24,7 +24,9 @@ public class InvoiceProfile : Profile
                     ? s.Customer.CompanyName
                     : $"{s.Customer.ContactFirstName} {s.Customer.ContactLastName}".Trim())
                 : string.Empty))
-            .ForMember(d => d.CustomerEmail, o => o.MapFrom(s => s.Customer != null ? s.Customer.Email : null))
+            .ForMember(d => d.CustomerEmail, o => o.MapFrom(s => s.Customer != null
+                ? (s.Customer.BillingEmail ?? s.Customer.Email)
+                : null))
             .ForMember(d => d.CustomerPhone, o => o.MapFrom(s => s.Customer != null ? s.Customer.Phone : null))
             .ForMember(d => d.CustomerNotifyByEmail, o => o.MapFrom(s => s.Customer == null || s.Customer.NotifyByEmail))
             .ForMember(d => d.PreparedByName, o => o.MapFrom(s => s.PreparedBy != null