📦 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-export.md

@@ -0,0 +1,45 @@
+# Disallow using `exports` in files containing tests (`no-export`)
+
+Prevents using `exports` if a file has one or more tests in it.
+
+## Rule Details
+
+This rule aims to eliminate duplicate runs of tests by exporting things from
+test files. If you import from a test file, then all the tests in that file will
+be run in each imported instance, so bottom line, don't export from a test, but
+instead move helper functions into a separate file when they need to be shared
+across tests.
+
+Examples of **incorrect** code for this rule:
+
+```js
+export function myHelper() {}
+
+module.exports = function () {};
+
+module.exports = {
+  something: 'that should be moved to a non-test file',
+};
+
+describe('a test', () => {
+  expect(1).toBe(1);
+});
+```
+
+Examples of **correct** code for this rule:
+
+```js
+function myHelper() {}
+
+const myThing = {
+  something: 'that can live here',
+};
+
+describe('a test', () => {
+  expect(1).toBe(1);
+});
+```
+
+## When Not To Use It
+
+Don't use this rule on non-jest test files.