chore: 补提测试修复、新增测试工具和设计文档

- fix(test): 同步 listInventory 签名（补 series/spec 参数）
- test(backend): 新增 import_parse_test.go
- chore(backend): 新增 cmd/test_xls 调试工具
- docs: UI 筛选组件设计规范、Gemini 项目配置

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

client/test/stock_out_insufficient_stock_flow_test.dart

@@ -95,6 +95,8 @@ class _FakeInventoryRepository extends InventoryRepository {
   Future<PageResult<Inventory>> listInventory({
     int? warehouseId,
     String? keyword,
+    List<String>? series,
+    List<String>? spec,
     int page = 1,
     int pageSize = 50,
   }) async {