📦 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/full/weak-map/delete-all.js

@@ -0,0 +1,6 @@
+'use strict';
+require('../../modules/es.weak-map');
+require('../../modules/esnext.weak-map.delete-all');
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('WeakMap', 'deleteAll');

frontend/node_modules/core-js-pure/full/weak-map/emplace.js

@@ -0,0 +1,6 @@
+'use strict';
+require('../../modules/es.weak-map');
+require('../../modules/esnext.weak-map.emplace');
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('WeakMap', 'emplace');

frontend/node_modules/core-js-pure/full/weak-map/from.js

@@ -0,0 +1,14 @@
+'use strict';
+require('../../modules/es.object.to-string');
+require('../../modules/es.array.iterator');
+require('../../modules/es.string.iterator');
+require('../../modules/es.weak-map');
+require('../../modules/esnext.weak-map.from');
+require('../../modules/esnext.weak-map.delete-all');
+require('../../modules/esnext.weak-map.emplace');
+require('../../modules/esnext.weak-map.get-or-insert');
+require('../../modules/esnext.weak-map.get-or-insert-computed');
+require('../../modules/web.dom-collections.iterator');
+var path = require('../../internals/path');
+
+module.exports = path.WeakMap.from;

frontend/node_modules/core-js-pure/full/weak-map/get-or-insert-computed.js

@@ -0,0 +1,4 @@
+'use strict';
+var parent = require('../../actual/weak-map/get-or-insert-computed');
+
+module.exports = parent;

frontend/node_modules/core-js-pure/full/weak-map/get-or-insert.js

@@ -0,0 +1,4 @@
+'use strict';
+var parent = require('../../actual/weak-map/get-or-insert');
+
+module.exports = parent;

frontend/node_modules/core-js-pure/full/weak-map/index.js

@@ -0,0 +1,13 @@
+'use strict';
+var parent = require('../../actual/weak-map');
+require('../../modules/es.string.iterator');
+require('../../modules/esnext.weak-map.from');
+require('../../modules/esnext.weak-map.of');
+require('../../modules/esnext.weak-map.emplace');
+require('../../modules/esnext.weak-map.get-or-insert');
+require('../../modules/esnext.weak-map.get-or-insert-computed');
+require('../../modules/esnext.weak-map.delete-all');
+// TODO: remove from `core-js@4`
+require('../../modules/esnext.weak-map.upsert');
+
+module.exports = parent;

frontend/node_modules/core-js-pure/full/weak-map/of.js

@@ -0,0 +1,12 @@
+'use strict';
+require('../../modules/es.object.to-string');
+require('../../modules/es.array.iterator');
+require('../../modules/es.weak-map');
+require('../../modules/esnext.weak-map.of');
+require('../../modules/esnext.weak-map.delete-all');
+require('../../modules/esnext.weak-map.emplace');
+require('../../modules/esnext.weak-map.get-or-insert');
+require('../../modules/esnext.weak-map.get-or-insert-computed');
+var path = require('../../internals/path');
+
+module.exports = path.WeakMap.of;

frontend/node_modules/core-js-pure/full/weak-map/upsert.js

@@ -0,0 +1,6 @@
+'use strict';
+require('../../modules/es.weak-map');
+require('../../modules/esnext.weak-map.upsert');
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('WeakMap', 'upsert');