Fix invoice ProjectName not pre-filling on edit; add to Details view

Edit GET now falls back to job.ProjectName for invoices created before the
column was added. Details view shows Project Name alongside Customer PO.

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

src/PowderCoating.Web/Controllers/InvoicesController.cs

@@ -903,7 +903,7 @@ public class InvoicesController : Controller
                 InternalNotes = invoice.InternalNotes,
                 Terms = invoice.Terms,
                 CustomerPO = invoice.CustomerPO,
-                ProjectName = invoice.ProjectName,
+                ProjectName = invoice.ProjectName ?? invoice.Job?.ProjectName,
                 InvoiceItems = invoice.InvoiceItems
                     .Where(i => !i.IsDeleted)
                     .OrderBy(i => i.DisplayOrder)

src/PowderCoating.Web/Views/Invoices/Details.cshtml

@@ -193,6 +193,13 @@
                                     <p class="mb-0">@Model.CustomerPO</p>
                                 </div>
                             }
+                            @if (!string.IsNullOrWhiteSpace(Model.ProjectName))
+                            {
+                                <div class="col-md-6">
+                                    <label class="text-muted small mb-1">Project Name</label>
+                                    <p class="mb-0">@Model.ProjectName</p>
+                                </div>
+                            }
                             @if (!string.IsNullOrWhiteSpace(Model.ExternalReference))
                             {
                                 <div class="col-md-6">