📦 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/features/object/assign.js

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+'use strict';
+module.exports = require('../../full/object/assign');

frontend/node_modules/core-js/features/object/create.js

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+'use strict';
+module.exports = require('../../full/object/create');

frontend/node_modules/core-js/features/object/define-getter.js

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+'use strict';
+module.exports = require('../../full/object/define-getter');

frontend/node_modules/core-js/features/object/define-properties.js

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+'use strict';
+module.exports = require('../../full/object/define-properties');

frontend/node_modules/core-js/features/object/define-property.js

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+'use strict';
+module.exports = require('../../full/object/define-property');

frontend/node_modules/core-js/features/object/define-setter.js

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+'use strict';
+module.exports = require('../../full/object/define-setter');

frontend/node_modules/core-js/features/object/entries.js

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+'use strict';
+module.exports = require('../../full/object/entries');

frontend/node_modules/core-js/features/object/freeze.js

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+'use strict';
+module.exports = require('../../full/object/freeze');

frontend/node_modules/core-js/features/object/from-entries.js

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+'use strict';
+module.exports = require('../../full/object/from-entries');

frontend/node_modules/core-js/features/object/get-own-property-descriptor.js

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+'use strict';
+module.exports = require('../../full/object/get-own-property-descriptor');

frontend/node_modules/core-js/features/object/get-own-property-descriptors.js

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+'use strict';
+module.exports = require('../../full/object/get-own-property-descriptors');

frontend/node_modules/core-js/features/object/get-own-property-names.js

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+'use strict';
+module.exports = require('../../full/object/get-own-property-names');

frontend/node_modules/core-js/features/object/get-own-property-symbols.js

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+'use strict';
+module.exports = require('../../full/object/get-own-property-symbols');

frontend/node_modules/core-js/features/object/get-prototype-of.js

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+'use strict';
+module.exports = require('../../full/object/get-prototype-of');

frontend/node_modules/core-js/features/object/group-by.js

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+'use strict';
+module.exports = require('../../full/object/group-by');

frontend/node_modules/core-js/features/object/has-own.js

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+'use strict';
+module.exports = require('../../full/object/has-own');

frontend/node_modules/core-js/features/object/index.js

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+'use strict';
+module.exports = require('../../full/object');

frontend/node_modules/core-js/features/object/is-extensible.js

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+'use strict';
+module.exports = require('../../full/object/is-extensible');

frontend/node_modules/core-js/features/object/is-frozen.js

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+'use strict';
+module.exports = require('../../full/object/is-frozen');

frontend/node_modules/core-js/features/object/is-sealed.js

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+'use strict';
+module.exports = require('../../full/object/is-sealed');

frontend/node_modules/core-js/features/object/is.js

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+'use strict';
+module.exports = require('../../full/object/is');

frontend/node_modules/core-js/features/object/iterate-entries.js

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+'use strict';
+module.exports = require('../../full/object/iterate-entries');

frontend/node_modules/core-js/features/object/iterate-keys.js

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+'use strict';
+module.exports = require('../../full/object/iterate-keys');

frontend/node_modules/core-js/features/object/iterate-values.js

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+'use strict';
+module.exports = require('../../full/object/iterate-values');

frontend/node_modules/core-js/features/object/keys.js

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+'use strict';
+module.exports = require('../../full/object/keys');

frontend/node_modules/core-js/features/object/lookup-getter.js

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+'use strict';
+module.exports = require('../../full/object/lookup-getter');

frontend/node_modules/core-js/features/object/lookup-setter.js

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+'use strict';
+module.exports = require('../../full/object/lookup-setter');

frontend/node_modules/core-js/features/object/prevent-extensions.js

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+'use strict';
+module.exports = require('../../full/object/prevent-extensions');

frontend/node_modules/core-js/features/object/proto.js

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+'use strict';
+module.exports = require('../../full/object/proto');

frontend/node_modules/core-js/features/object/seal.js

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+'use strict';
+module.exports = require('../../full/object/seal');

frontend/node_modules/core-js/features/object/set-prototype-of.js

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+'use strict';
+module.exports = require('../../full/object/set-prototype-of');

frontend/node_modules/core-js/features/object/to-string.js

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+'use strict';
+module.exports = require('../../full/object/to-string');

frontend/node_modules/core-js/features/object/values.js

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+'use strict';
+module.exports = require('../../full/object/values');