📦 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/lib/rules/utils/unicode/is-combining-character.js

@@ -0,0 +1,13 @@
+/**
+ * @author Toru Nagashima <https://github.com/mysticatea>
+ */
+"use strict";
+
+/**
+ * Check whether a given character is a combining mark or not.
+ * @param {number} codePoint The character code to check.
+ * @returns {boolean} `true` if the character belongs to the category, any of `Mc`, `Me`, and `Mn`.
+ */
+module.exports = function isCombiningCharacter(codePoint) {
+    return /^[\p{Mc}\p{Me}\p{Mn}]$/u.test(String.fromCodePoint(codePoint));
+};