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/EquipmentManualService.cs

@@ -56,25 +56,16 @@ public class EquipmentManualService : IEquipmentManualService
     /// </returns>
     public async Task<(bool Success, string FilePath, string ErrorMessage)> SaveEquipmentManualAsync(IFormFile file, int companyId, int equipmentId)
     {
-        if (file == null || file.Length == 0)
-            return (false, string.Empty, "No file provided");
-
-        if (file.Length > MaxFileSize)
-            return (false, string.Empty, $"File size exceeds maximum allowed size of {MaxFileSize / 1024 / 1024} MB");
-
-        var extension = Path.GetExtension(file.FileName).ToLowerInvariant();
-        if (!AllowedExtensions.Contains(extension))
-            return (false, string.Empty, $"File type not allowed. Allowed types: {string.Join(", ", AllowedExtensions)}");
+        var (isValid, extension, error) = BlobFileHelper.ValidateUpload(file, AllowedExtensions, MaxFileSize);
+        if (!isValid)
+            return (false, string.Empty, error);
 
         // Sanitize filename — replace OS-invalid characters with underscores to
         // prevent path traversal and blob naming errors in Azure.
-        var fileName = Path.GetFileNameWithoutExtension(file.FileName);
-        fileName = string.Join("_", fileName.Split(Path.GetInvalidFileNameChars()));
-        if (string.IsNullOrWhiteSpace(fileName))
-            fileName = "manual";
+        var fileName = BlobFileHelper.SanitizeFileName(Path.GetFileNameWithoutExtension(file.FileName));
 
         var blobName = $"{companyId}/equipment-manuals/{equipmentId}/{fileName}{extension}";
-        var contentType = GetContentType(extension);
+        var contentType = BlobFileHelper.GetContentType(extension);
 
         using var stream = file.OpenReadStream();
         var result = await _blobService.UploadAsync(_settings.Containers.Manuals, blobName, stream, contentType);
@@ -130,19 +121,4 @@ public class EquipmentManualService : IEquipmentManualService
         return await _blobService.ExistsAsync(_settings.Containers.Manuals, filePath);
     }
 
-    /// <summary>
-    /// Maps a lowercase file extension to its canonical MIME content type.
-    /// Correct MIME types are required so browsers open PDFs inline and
-    /// Word documents prompt a compatible application rather than a raw download.
-    /// </summary>
-    /// <param name="extension">Lowercase file extension including the leading dot.</param>
-    /// <returns>MIME type string, or <c>application/octet-stream</c> as a safe fallback.</returns>
-    private static string GetContentType(string extension) => extension switch
-    {
-        ".pdf" => "application/pdf",
-        ".doc" => "application/msword",
-        ".docx" => "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
-        ".txt" => "text/plain",
-        _ => "application/octet-stream"
-    };
 }