📦 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/core-js-pure/modules/es.array.reduce-right.js

@@ -0,0 +1,19 @@
+'use strict';
+var $ = require('../internals/export');
+var $reduceRight = require('../internals/array-reduce').right;
+var arrayMethodIsStrict = require('../internals/array-method-is-strict');
+var CHROME_VERSION = require('../internals/environment-v8-version');
+var IS_NODE = require('../internals/environment-is-node');
+
+// Chrome 80-82 has a critical bug
+// https://bugs.chromium.org/p/chromium/issues/detail?id=1049982
+var CHROME_BUG = !IS_NODE && CHROME_VERSION > 79 && CHROME_VERSION < 83;
+var FORCED = CHROME_BUG || !arrayMethodIsStrict('reduceRight');
+
+// `Array.prototype.reduceRight` method
+// https://tc39.es/ecma262/#sec-array.prototype.reduceright
+$({ target: 'Array', proto: true, forced: FORCED }, {
+  reduceRight: function reduceRight(callbackfn /* , initialValue */) {
+    return $reduceRight(this, callbackfn, arguments.length, arguments.length > 1 ? arguments[1] : undefined);
+  }
+});