📦 添加虚拟环境和启动脚本

新增:
- backend/venv/ - Python 虚拟环境
- backend/start.sh - 启动脚本（使用虚拟环境）
- backend/requirements.txt - 依赖列表
- .gitignore - 忽略虚拟环境和缓存文件

说明:
- 每个项目使用独立虚拟环境
- 避免依赖冲突
- 启动脚本自动创建和激活虚拟环境

frontend/node_modules/eslint-plugin-jest/docs/rules/no-mocks-import.md

@@ -0,0 +1,27 @@
+# Disallow manually importing from `__mocks__` (`no-mocks-import`)
+
+When using `jest.mock`, your tests (just like the code being tested) should
+import from `./x`, not `./__mocks__/x`. Not following this rule can lead to
+confusion, because you will have multiple instances of the mocked module:
+
+```js
+jest.mock('./x');
+const x1 = require('./x');
+const x2 = require('./__mocks__/x');
+
+test('x', () => {
+  expect(x1).toBe(x2); // fails! They are both instances of `./__mocks__/x`, but not referentially equal
+});
+```
+
+### Rule details
+
+This rule reports imports from a path containing a `__mocks__` component.
+
+Example violations:
+
+```js
+import thing from './__mocks__/index';
+require('./__mocks__/index');
+require('__mocks__');
+```