feat: Improve bulk category update functionality with validation and clearer logic

backend/src/products/products.service.ts

@@ -389,12 +389,15 @@ export class ProductsService {
 
   async bulkUpdate(ids: number[], data: { categoryId?: number | null }) {
     const updateData: Record<string, any> = {};
-    if ('categoryId' in data) {
+    if (data.categoryId !== undefined) {
       updateData.categoryId = data.categoryId;
     }
     if (Object.keys(updateData).length === 0) return { updated: 0 };
-    await this.prisma.product.updateMany({ where: { id: { in: ids } }, data: updateData });
-    return { updated: ids.length };
+    const result = await this.prisma.product.updateMany({
+      where: { id: { in: ids } },
+      data: updateData,
+    });
+    return { updated: result.count };
   }
 
   async findUncategorized(): Promise<{ id: number; name: string; canonicalName: string | null }[]> {

flutter/lib/features/admin/presentation/admin_products_panel.dart

@@ -104,14 +104,21 @@ class _AdminProductsPanelState extends ConsumerState<AdminProductsPanel> {
 
   Future<void> _applyBulkCategory() async {
     if (_selectedIds.isEmpty || _isApplying) return;
+    if (_bulkCategoryValue == null) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(content: Text('Välj en kategori innan du uppdaterar valda produkter.')),
+      );
+      return;
+    }
+
+    final categoryId =
+        _bulkCategoryValue == '__remove__' ? null : int.parse(_bulkCategoryValue!);
+
     setState(() => _isApplying = true);
     try {
       await ref.read(adminRepositoryProvider).bulkSetCategory(
             _selectedIds.toList(),
-            categoryId: _bulkCategoryValue == null ||
-                    _bulkCategoryValue == '__remove__'
-                ? null
-                : int.parse(_bulkCategoryValue!),
+            categoryId: categoryId,
           );
       if (!mounted) return;
       setState(() {
@@ -651,7 +658,9 @@ class _AdminProductsPanelState extends ConsumerState<AdminProductsPanel> {
               ),
             if (!_showDeletedOnly)
               FilledButton(
-                onPressed: _selectedIds.isEmpty || _isApplying
+                onPressed: _selectedIds.isEmpty ||
+                        _isApplying ||
+                        _bulkCategoryValue == null
                     ? null
                     : _applyBulkCategory,
                 child: _isApplying