fix: use dialog context in product delete confirmation

Navigator.pop(context) with the outer tile context caused go_router to
pop the main navigation stack instead of closing the dialog. Use the
builder's ctx parameter instead.

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

client/lib/features/products/products_screen.dart

@@ -176,16 +176,16 @@ class _ProductTile extends ConsumerWidget {
       confirmDismiss: (_) async {
         return await showDialog<bool>(
           context: context,
-          builder: (_) => AlertDialog(
+          builder: (ctx) => AlertDialog(
             title: const Text('Удалить продукт?'),
             content: Text('«${product.name}» будет удалён из списка.'),
             actions: [
               TextButton(
-                onPressed: () => Navigator.pop(context, false),
+                onPressed: () => Navigator.pop(ctx, false),
                 child: const Text('Отмена'),
               ),
               TextButton(
-                onPressed: () => Navigator.pop(context, true),
+                onPressed: () => Navigator.pop(ctx, true),
                 child: const Text('Удалить'),
               ),
             ],