fix: filter null names in multi-choice attributes and use loading spinner cell

- Filter out null/empty names in AssignedMultiChoiceAttribute before
  joining to avoid leading/trailing separators
- Replace text placeholder "..." with proper loadingCell() spinner
  for attribute columns while data is being fetched

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lkostrowski

src/attributes/utils/assignedAttributes.ts

@@ -9,7 +9,10 @@ export function getDisplayValueFromAssignedAttribute(attr: AssignedAttributeItem
     case "AssignedSingleChoiceAttribute":
       return attr.singleChoiceValue?.name ?? "";
     case "AssignedMultiChoiceAttribute":
-      return attr.multiChoiceValue.map((v: { name: string | null }) => v.name).join(", ");
+      return attr.multiChoiceValue
+        .map((v: { name: string | null }) => v.name?.trim())
+        .filter((name): name is string => !!name)
+        .join(", ");
     case "AssignedNumericAttribute":
       return attr.numericValue != null ? String(attr.numericValue) : "";
     case "AssignedPlainTextAttribute":

src/products/components/ProductListDatagrid/datagrid.ts

@@ -9,6 +9,7 @@ import {
 import { type ColumnCategory } from "@dashboard/components/Datagrid/ColumnPicker/useColumns";
 import {
   dateCell,
+  loadingCell,
   moneyCell,
   pillCell,
   readonlyTextCell,
@@ -390,7 +391,7 @@ function getAttributeCellContent(
   attributesLoading?: boolean,
 ) {
   if (attributesLoading) {
-    return readonlyTextCell("...", true, "faded");
+    return loadingCell();
   }
 
   if (!productId || !getAssignedAttribute) {