📦 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/es/function/bind.js

@@ -0,0 +1,5 @@
+'use strict';
+require('../../modules/es.function.bind');
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('Function', 'bind');

frontend/node_modules/core-js-pure/es/function/has-instance.js

@@ -0,0 +1,5 @@
+'use strict';
+require('../../modules/es.function.has-instance');
+var wellKnownSymbol = require('../../internals/well-known-symbol');
+
+module.exports = Function[wellKnownSymbol('hasInstance')];

frontend/node_modules/core-js-pure/es/function/index.js

@@ -0,0 +1,7 @@
+'use strict';
+require('../../modules/es.function.bind');
+require('../../modules/es.function.name');
+require('../../modules/es.function.has-instance');
+var path = require('../../internals/path');
+
+module.exports = path.Function;

frontend/node_modules/core-js-pure/es/function/name.js

@@ -0,0 +1,2 @@
+'use strict';
+require('../../modules/es.function.name');

frontend/node_modules/core-js-pure/es/function/virtual/bind.js

@@ -0,0 +1,5 @@
+'use strict';
+require('../../../modules/es.function.bind');
+var getBuiltInPrototypeMethod = require('../../../internals/get-built-in-prototype-method');
+
+module.exports = getBuiltInPrototypeMethod('Function', 'bind');

frontend/node_modules/core-js-pure/es/function/virtual/index.js

@@ -0,0 +1,5 @@
+'use strict';
+require('../../../modules/es.function.bind');
+var entryVirtual = require('../../../internals/entry-virtual');
+
+module.exports = entryVirtual('Function');