📦 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/@babel/preset-modules/lib/plugins/transform-async-arrows-in-class/index.js

@@ -0,0 +1,45 @@
+"use strict";
+
+exports.__esModule = true;
+exports.default = void 0;
+
+/**
+ * Safari 10.3 had an issue where async arrow function expressions within any class method would throw.
+ * After an initial fix, any references to the instance via `this` within those methods would also throw.
+ * This is fixed by converting arrow functions in class methods into equivalent function expressions.
+ * @see https://bugs.webkit.org/show_bug.cgi?id=166879
+ *
+ * @example
+ *   class X{ a(){ async () => {}; } }   // throws
+ *   class X{ a(){ async function() {}; } }   // works
+ *
+ * @example
+ *   class X{ a(){
+ *     async () => this.a;   // throws
+ *   } }
+ *   class X{ a(){
+ *     var _this=this;
+ *     async function() { return _this.a };   // works
+ *   } }
+ */
+const OPTS = {
+  allowInsertArrow: false,
+  specCompliant: false
+};
+
+var _default = ({
+  types: t
+}) => ({
+  name: "transform-async-arrows-in-class",
+  visitor: {
+    ArrowFunctionExpression(path) {
+      if (path.node.async && path.findParent(t.isClassMethod)) {
+        path.arrowFunctionToExpression(OPTS);
+      }
+    }
+
+  }
+});
+
+exports.default = _default;
+module.exports = exports.default;