Refactor: extract shared helpers, fix field drift, add assembly services

- IJobItemAssemblyService / IQuotePricingAssemblyService: centralize job item
  and quote pricing construction that was duplicated across create, rework copy,
  and quote-to-job conversion paths
- BlobFileHelper: single ValidateUpload/GetContentType/SanitizeFileName used by
  6 blob services (JobPhoto, QuotePhoto, ProfilePhoto, CompanyLogo, Equipment,
  Catalog) and BillsController + ExpensesController, removing 8 private copies
- PagedResult<T>.From(): static factory eliminates 6-line boilerplate in 11
  controllers (Appointments, Customers, Equipment, Inventory, Invoices, Jobs,
  Maintenance, CompanyUsers, PlatformUsers, Quotes, Vendors)
- AccountingDropdownHelper: single LoadAsync() call replaces duplicate
  vendor/account/job queries in BillsController and ExpensesController
- JobTemplateItem: add IsSalesItem + Sku fields with migration; propagate
  through JobTemplatesController snapshot copy and GetTemplatesJson projection,
  and JobsController template-application path
- Test assertions updated for standardized BlobFileHelper error messages

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

src/PowderCoating.Application/Interfaces/IJobItemAssemblyService.cs

@@ -0,0 +1,19 @@
+using PowderCoating.Application.DTOs.Quote;
+using PowderCoating.Core.Entities;
+
+namespace PowderCoating.Application.Interfaces;
+
+public interface IJobItemAssemblyService
+{
+    JobItem CreateJobItem(CreateQuoteItemDto source, int jobId, int companyId, QuoteItemPricingResult pricing, DateTime createdAtUtc);
+    IReadOnlyList<JobItemCoat> CreateJobItemCoats(CreateQuoteItemDto source, int jobItemId, int companyId, DateTime createdAtUtc);
+    IReadOnlyList<JobItemPrepService> CreateJobItemPrepServices(CreateQuoteItemDto source, int jobItemId, int companyId, DateTime createdAtUtc);
+
+    JobItem CreateJobItem(QuoteItem source, int jobId, int companyId, DateTime createdAtUtc);
+    IReadOnlyList<JobItemCoat> CreateJobItemCoats(QuoteItem source, int jobItemId, int companyId, DateTime createdAtUtc);
+    IReadOnlyList<JobItemPrepService> CreateJobItemPrepServices(QuoteItem source, int jobItemId, int companyId, DateTime createdAtUtc);
+
+    JobItem CreateJobItem(JobItem source, int jobId, int companyId, DateTime createdAtUtc);
+    IReadOnlyList<JobItemCoat> CreateJobItemCoats(JobItem source, int jobItemId, int companyId, DateTime createdAtUtc);
+    IReadOnlyList<JobItemPrepService> CreateJobItemPrepServices(JobItem source, int jobItemId, int companyId, DateTime createdAtUtc);
+}

src/PowderCoating.Application/Interfaces/IQuotePricingAssemblyService.cs

@@ -0,0 +1,16 @@
+using PowderCoating.Application.DTOs.Quote;
+using PowderCoating.Core.Entities;
+
+namespace PowderCoating.Application.Interfaces;
+
+public interface IQuotePricingAssemblyService
+{
+    void ApplyPricingSnapshot(Quote quote, QuotePricingResult pricingResult);
+
+    Task<IReadOnlyList<QuoteItem>> CreateQuoteItemsAsync(
+        IEnumerable<CreateQuoteItemDto> itemDtos,
+        int quoteId,
+        int companyId,
+        decimal? ovenRateOverride,
+        DateTime createdAtUtc);
+}