feat(edit): 编辑页样式修改

apps/web/src/pages/products/ProductEditPage.css

@@ -12,6 +12,13 @@
     padding-bottom: 92px;
 }
 
+/* 编辑器快照加载前占满内容可视区，避免加载图标受页面留白影响而偏移。 */
+.product-editor-loading {
+    display: grid;
+    min-height: calc(100vh - 90px);
+    place-items: center;
+}
+
 /* 页头 */
 .editor-header {
     margin: -4px 0 20px;

apps/web/src/pages/products/ProductEditPage.tsx

@@ -870,7 +870,11 @@ const ProductEditPage = () => {
 
     if (!currentPlatform) return <Alert type="warning" message="正在读取平台上下文" />;
     if (loading && !snapshot)
-        return <Spin size="large" style={{ display: 'block', margin: '72px auto' }} />;
+        return (
+            <div className="product-editor-loading">
+                <Spin size="large" />
+            </div>
+        );
     if (!snapshot)
         return (
             <Alert