📦 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/prefer-to-be.md

@@ -0,0 +1,53 @@
+# Suggest using `toBe()` for primitive literals (`prefer-to-be`)
+
+When asserting against primitive literals such as numbers and strings, the
+equality matchers all operate the same, but read slightly differently in code.
+
+This rule recommends using the `toBe` matcher in these situations, as it forms
+the most grammatically natural sentence. For `null`, `undefined`, and `NaN` this
+rule recommends using their specific `toBe` matchers, as they give better error
+messages as well.
+
+## Rule details
+
+This rule triggers a warning if `toEqual()` or `toStrictEqual()` are used to
+assert a primitive literal value such as numbers, strings, and booleans.
+
+The following patterns are considered warnings:
+
+```js
+expect(value).not.toEqual(5);
+expect(getMessage()).toStrictEqual('hello world');
+expect(loadMessage()).resolves.toEqual('hello world');
+```
+
+The following pattern is not warning:
+
+```js
+expect(value).not.toBe(5);
+expect(getMessage()).toBe('hello world');
+expect(loadMessage()).resolves.toBe('hello world');
+expect(didError).not.toBe(true);
+
+expect(catchError()).toStrictEqual({ message: 'oh noes!' });
+```
+
+For `null`, `undefined`, and `NaN`, this rule triggers a warning if `toBe` is
+used to assert against those literal values instead of their more specific
+`toBe` counterparts:
+
+```js
+expect(value).not.toBe(undefined);
+expect(getMessage()).toBe(null);
+expect(countMessages()).resolves.not.toBe(NaN);
+```
+
+The following pattern is not warning:
+
+```js
+expect(value).toBeDefined();
+expect(getMessage()).toBeNull();
+expect(countMessages()).resolves.not.toBeNaN();
+
+expect(catchError()).toStrictEqual({ message: undefined });
+```