Add Project Name field to invoice create and edit forms

Stores ProjectName on the Invoice entity (previously only inherited from the
linked job at display time). Pre-fills from the job when creating from a job.
Migration: AddInvoiceProjectName.

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

src/PowderCoating.Web/Controllers/InvoicesController.cs

@@ -372,6 +372,7 @@ public class InvoicesController : Controller
                 dto.JobId = job.Id;
                 dto.CustomerId = job.CustomerId;
                 dto.CustomerPO = job.CustomerPO;
+                dto.ProjectName = job.ProjectName;
 
                 // Resolve catalog item revenue accounts for pre-population
                 var catalogItemIds = job.JobItems
@@ -710,6 +711,7 @@ public class InvoicesController : Controller
                 InternalNotes = dto.InternalNotes,
                 Terms = dto.Terms,
                 CustomerPO = dto.CustomerPO,
+                ProjectName = dto.ProjectName,
                 CompanyId = currentUser.CompanyId,
                 CreatedAt = DateTime.UtcNow,
                 CreatedBy = currentUser.Email
@@ -901,6 +903,7 @@ public class InvoicesController : Controller
                 InternalNotes = invoice.InternalNotes,
                 Terms = invoice.Terms,
                 CustomerPO = invoice.CustomerPO,
+                ProjectName = invoice.ProjectName,
                 InvoiceItems = invoice.InvoiceItems
                     .Where(i => !i.IsDeleted)
                     .OrderBy(i => i.DisplayOrder)
@@ -1036,6 +1039,7 @@ public class InvoicesController : Controller
             invoice.InternalNotes = dto.InternalNotes;
             invoice.Terms = dto.Terms;
             invoice.CustomerPO = dto.CustomerPO;
+            invoice.ProjectName = dto.ProjectName;
             invoice.UpdatedAt = DateTime.UtcNow;
             invoice.UpdatedBy = currentUser?.Email;