Add CRM features: Additional Contacts, Lead Source, Ship-To Address; update Help docs

- New CustomerContact entity + migration (AddCustomerContactsAndCrmFields)
- Customer.LeadSource + ShipToAddress/City/State/ZipCode/Country fields
- Additional Contacts card on Customer Details with AJAX add/edit/delete
- Lead Source dropdown on Create/Edit; Ship-To section on Create/Edit
- Customer Details: side-by-side billing/ship-to when ship-to is set
- Help docs: Customers (contacts, ship-to, lead source, preferred powders, outstanding pickups)
- Help docs: Jobs (clone job, project name), Quotes (project name), Invoices (project name), Inventory (low stock clickable filter)
- HelpKnowledgeBase.cs updated for all features above

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

src/PowderCoating.Application/Mappings/CustomerProfile.cs

@@ -41,5 +41,12 @@ public class CustomerProfile : Profile
                       opt => opt.MapFrom(src => !string.IsNullOrEmpty(src.ContactFirstName) || !string.IsNullOrEmpty(src.ContactLastName)
                           ? $"{src.ContactFirstName} {src.ContactLastName}".Trim()
                           : string.Empty));
+
+        // CustomerContact
+        CreateMap<CustomerContact, CustomerContactDto>();
+        CreateMap<CreateCustomerContactDto, CustomerContact>();
+        CreateMap<UpdateCustomerContactDto, CustomerContact>()
+            .ForMember(dest => dest.Id, opt => opt.Ignore()); // Id is set by the controller, not mapped
+        CreateMap<CustomerContact, UpdateCustomerContactDto>();
     }
 }