📦 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/modules/es.json.raw-json.js

@@ -0,0 +1,39 @@
+'use strict';
+var $ = require('../internals/export');
+var FREEZING = require('../internals/freezing');
+var NATIVE_RAW_JSON = require('../internals/native-raw-json');
+var getBuiltIn = require('../internals/get-built-in');
+var uncurryThis = require('../internals/function-uncurry-this');
+var toString = require('../internals/to-string');
+var createProperty = require('../internals/create-property');
+var setInternalState = require('../internals/internal-state').set;
+
+var $SyntaxError = SyntaxError;
+var parse = getBuiltIn('JSON', 'parse');
+var create = getBuiltIn('Object', 'create');
+var freeze = getBuiltIn('Object', 'freeze');
+var at = uncurryThis(''.charAt);
+
+var ERROR_MESSAGE = 'Unacceptable as raw JSON';
+
+var isWhitespace = function (it) {
+  return it === ' ' || it === '\t' || it === '\n' || it === '\r';
+};
+
+// `JSON.rawJSON` method
+// https://tc39.es/proposal-json-parse-with-source/#sec-json.rawjson
+// https://github.com/tc39/proposal-json-parse-with-source
+$({ target: 'JSON', stat: true, forced: !NATIVE_RAW_JSON }, {
+  rawJSON: function rawJSON(text) {
+    var jsonString = toString(text);
+    if (jsonString === '' || isWhitespace(at(jsonString, 0)) || isWhitespace(at(jsonString, jsonString.length - 1))) {
+      throw new $SyntaxError(ERROR_MESSAGE);
+    }
+    var parsed = parse(jsonString);
+    if (typeof parsed == 'object' && parsed !== null) throw new $SyntaxError(ERROR_MESSAGE);
+    var obj = create(null);
+    setInternalState(obj, { type: 'RawJSON' });
+    createProperty(obj, 'rawJSON', jsonString);
+    return FREEZING ? freeze(obj) : obj;
+  }
+});