Label blank account option "(None)" when no company default is set

The item account dropdowns showed "(Default … account)" on the blank
option even when the company hadn't configured a default — implying a
fallback that didn't exist. Now the blank option reads "(None)" unless a
matching company default is configured, in which case it keeps the
"(Default …)" label (the dropdown pre-selects the real account anyway).
"Has default" flags are computed in the shared dropdown-population helpers
so every render path (Create/Edit GET and invalid-POST) gets them.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Web/Controllers/InventoryController.cs

@@ -1667,6 +1667,13 @@ public class InventoryController : Controller
             .OrderBy(a => a.AccountNumber)
             .Select(a => new SelectListItem($"{a.AccountNumber} – {a.Name}", a.Id.ToString()))
             .ToList();
+
+        // Whether the company has configured default accounts — the views use this to label the
+        // blank dropdown option "(Default …)" vs "(None)".
+        var prefs = await _unitOfWork.CompanyPreferences
+            .FirstOrDefaultAsync(p => p.CompanyId == companyId && !p.IsDeleted);
+        ViewBag.HasDefaultInventoryAccount = prefs?.DefaultInventoryAccountId != null;
+        ViewBag.HasDefaultCogsAccount      = prefs?.DefaultCogsAccountId != null;
     }
 
     /// <summary>