Mobile layout fix for Job Details items; coat color on invoice line items

- Job Details: hide desktop item tables on mobile (d-none d-lg-block) so only
  the existing mobile-card layout shows on small screens — prevents 20-line rows
  on a narrow phone display
- Invoices Create (ForJob path): load job item coats and derive ColorName from
  coat colors when the item itself has no explicit color set; multiple coats join
  as 'Color1 / Color2' — lets customers distinguish repeated items (e.g. multiple
  caliper sets) on the invoice

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

src/PowderCoating.Web/Controllers/InvoicesController.cs

@@ -355,6 +355,15 @@ public class InvoicesController : Controller
                 var job = await _unitOfWork.Jobs.GetByIdAsync(jobId.Value, false, j => j.Customer, j => j.JobItems);
                 if (job == null) return NotFound();
 
+                // Pre-load coats so we can derive color names for invoice line items
+                var activeItemIds = job.JobItems.Where(ji => !ji.IsDeleted).Select(ji => ji.Id).ToList();
+                var allCoats = activeItemIds.Any()
+                    ? (await _unitOfWork.JobItemCoats.FindAsync(c => activeItemIds.Contains(c.JobItemId) && !c.IsDeleted)).ToList()
+                    : new List<JobItemCoat>();
+                var coatsByItem = allCoats
+                    .GroupBy(c => c.JobItemId)
+                    .ToDictionary(g => g.Key, g => g.OrderBy(c => c.Sequence).ToList());
+
                 // Validate no existing active invoice for this job (voided ones are kept as history)
                 var existing = await _unitOfWork.Invoices.GetForJobAsync(jobId.Value);
                 if (existing != null && existing.Status != InvoiceStatus.Voided)
@@ -404,6 +413,16 @@ public class InvoicesController : Controller
                         revenueAccountId = ci.RevenueAccountId;
                     revenueAccountId ??= defaultRevenueAccount?.Id;
 
+                    // Derive color from coats when the item itself has no explicit color set
+                    var derivedColor = item.ColorName;
+                    if (string.IsNullOrEmpty(derivedColor) && coatsByItem.TryGetValue(item.Id, out var itemCoats))
+                    {
+                        var coatColors = itemCoats
+                            .Where(c => !string.IsNullOrEmpty(c.ColorName))
+                            .Select(c => c.ColorName!);
+                        derivedColor = string.Join(" / ", coatColors);
+                    }
+
                     dto.InvoiceItems.Add(new CreateInvoiceItemDto
                     {
                         SourceJobItemId  = item.Id,
@@ -412,7 +431,7 @@ public class InvoicesController : Controller
                         Quantity         = item.Quantity > 0 ? item.Quantity : 1,
                         UnitPrice        = item.UnitPrice,
                         TotalPrice       = item.TotalPrice,
-                        ColorName        = item.ColorName,
+                        ColorName        = derivedColor,
                         Notes            = item.Notes,
                         DisplayOrder     = order++,
                         RevenueAccountId = revenueAccountId