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/Services/QuotePhotoService.cs

@@ -50,19 +50,13 @@ public class QuotePhotoService : IQuotePhotoService
     public async Task<(bool Success, string TempId, string FilePath, string ErrorMessage)> SaveTempPhotoAsync(
         IFormFile file, int companyId)
     {
-        if (file == null || file.Length == 0)
-            return (false, string.Empty, string.Empty, "No file provided.");
-
-        if (file.Length > MaxFileSizeBytes)
-            return (false, string.Empty, string.Empty, "File exceeds the 10 MB limit.");
-
-        var ext = Path.GetExtension(file.FileName).ToLowerInvariant();
-        if (!AllowedExtensions.Contains(ext))
-            return (false, string.Empty, string.Empty, $"File type '{ext}' is not allowed.");
+        var (isValid, ext, validationError) = BlobFileHelper.ValidateUpload(file, AllowedExtensions, MaxFileSizeBytes);
+        if (!isValid)
+            return (false, string.Empty, string.Empty, validationError);
 
         var tempId = Guid.NewGuid().ToString("N");
         var blobName = $"temp/{tempId}/{Guid.NewGuid():N}{ext}";
-        var contentType = GetContentType(ext);
+        var contentType = BlobFileHelper.GetContentType(ext);
 
         using var stream = file.OpenReadStream();
         var result = await _blobService.UploadAsync(_settings.Containers.QuoteImages, blobName, stream, contentType);
@@ -100,7 +94,7 @@ public class QuotePhotoService : IQuotePhotoService
             return (false, string.Empty, "Failed to read temp photo.");
 
         using var ms = new MemoryStream(download.Content);
-        var upload = await _blobService.UploadAsync(_settings.Containers.QuoteImages, destBlob, ms, GetContentType(ext));
+        var upload = await _blobService.UploadAsync(_settings.Containers.QuoteImages, destBlob, ms, BlobFileHelper.GetContentType(ext));
         if (!upload.Success)
             return (false, string.Empty, "Failed to save permanent photo.");
 
@@ -173,12 +167,4 @@ public class QuotePhotoService : IQuotePhotoService
         }
     }
 
-    private static string GetContentType(string ext) => ext switch
-    {
-        ".jpg" or ".jpeg" => "image/jpeg",
-        ".png" => "image/png",
-        ".gif" => "image/gif",
-        ".webp" => "image/webp",
-        _ => "image/jpeg"
-    };
 }