Add Custom Powder Order line item and fix CSV import FinalPrice crash

Custom powder/incoming powder material cost now flows into a separate
auto-generated 'Custom Powder Order' line item instead of rolling into
individual item prices, so users can add shipping charges before the
customer sees the total. A dashed yellow preview card in the wizard
shows the material cost and lets users edit the total (including shipping)
before saving. After first save the price is user-owned.

Also fixes a fatal CSV import crash when FinalPrice contains a non-numeric
value (e.g. 'false' from a spreadsheet formula): the job CSV importer now
streams rows one at a time with a lenient decimal converter, treating bad
values as $0 with a per-row warning instead of aborting the entire import.

Updated HelpKnowledgeBase.cs and Help articles (Jobs, Quotes) with
Custom Powder Order behavior and a new Data Import / Export section.

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

src/PowderCoating.Application/Mappings/QuoteProfile.cs

@@ -192,7 +192,10 @@ public class QuoteProfile : Profile
             .ForMember(dest => dest.UpdatedBy, opt => opt.Ignore());
 
         // QuoteItem -> CreateQuoteItemDto (for Edit view)
+        // Coats and PrepServices must be mapped explicitly; convention-based collection mapping
+        // is unreliable for ICollection<T> → List<T2> with different element types.
         CreateMap<QuoteItem, CreateQuoteItemDto>()
+            .ForMember(dest => dest.Coats, opt => opt.MapFrom(src => src.Coats))
             .ForMember(dest => dest.PrepServices, opt => opt.MapFrom(src => src.PrepServices));
 
         // ============================================================================