📦 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/jsx-ast-utils/lib/values/expressions/SequenceExpression.js

@@ -0,0 +1,21 @@
+'use strict';
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = extractValueFromSequenceExpression;
+/**
+ * Extractor function for a SequenceExpression type value node.
+ * A Sequence expression is an object with an attribute named
+ * expressions which contains an array of different types
+ *  of expression objects.
+ *
+ * @returns - An array of the extracted elements.
+ */
+function extractValueFromSequenceExpression(value) {
+  // eslint-disable-next-line global-require
+  var getValue = require('.').default;
+  return value.expressions.map(function (element) {
+    return getValue(element);
+  });
+}