📦 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-safari-block-shadowing/index.js

@@ -0,0 +1,47 @@
+"use strict";
+
+exports.__esModule = true;
+exports.default = _default;
+
+/**
+ * Fixes block-shadowed let/const bindings in Safari 10/11.
+ * https://kangax.github.io/compat-table/es6/#test-let_scope_shadow_resolution
+ */
+function _default({
+  types: t
+}) {
+  return {
+    name: "transform-safari-block-shadowing",
+    visitor: {
+      VariableDeclarator(path) {
+        // the issue only affects let and const bindings:
+        const kind = path.parent.kind;
+        if (kind !== "let" && kind !== "const") return; // ignore non-block-scoped bindings:
+
+        const block = path.scope.block;
+        if (t.isFunction(block) || t.isProgram(block)) return;
+        const bindings = t.getOuterBindingIdentifiers(path.node.id);
+
+        for (const name of Object.keys(bindings)) {
+          let scope = path.scope; // ignore parent bindings (note: impossible due to let/const?)
+
+          if (!scope.hasOwnBinding(name)) continue; // check if shadowed within the nearest function/program boundary
+
+          while (scope = scope.parent) {
+            if (scope.hasOwnBinding(name)) {
+              path.scope.rename(name);
+              break;
+            }
+
+            if (t.isFunction(scope.block) || t.isProgram(scope.block)) {
+              break;
+            }
+          }
+        }
+      }
+
+    }
+  };
+}
+
+module.exports = exports.default;