test(select): pin dropdown visual contract

变更摘要：

- 为共享 Select 补充最终视觉契约回归测试，覆盖下拉阴影和选项层级

- 保持范围收敛，仅强化 shared contract，不改生产代码

- 已运行共享测试、lint 和 build 进行回归验证

关键文件：

- web/src/shared/ui/select.test.ts

web/src/shared/ui/select.test.ts

@@ -25,6 +25,12 @@ describe('shared select contract', () => {
     expect(SELECT_ITEM_CLASS_NAME).toContain('data-[disabled]:opacity-50')
   })
 
+  it('keeps the dropdown and selected items visually discoverable', () => {
+    expect(SELECT_CONTENT_CLASS_NAME).toContain('shadow-md')
+    expect(SELECT_ITEM_CLASS_NAME).toContain('pl-8')
+    expect(SELECT_ITEM_CLASS_NAME).toContain('rounded-md')
+  })
+
   it('maps empty and nullish form state to an undefined Radix value', () => {
     expect(normalizeSelectValue('')).toBeUndefined()
     expect(normalizeSelectValue(null)).toBeUndefined()