📦 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/adjust-sourcemap-loader/lib/loader.js

@@ -0,0 +1,40 @@
+'use strict';
+
+var path = require('path');
+
+var loaderUtils = require('loader-utils');
+
+var process = require('./process');
+
+/**
+ * Webpack loader that manipulates the source-map of a preceding loader.
+ * @this {object} The loader context
+ * @param {string} content The content
+ * @param {object} sourceMap The source-map
+ * @returns {string|String}
+ */
+function loader(content, sourceMap) {
+  /* jshint validthis:true */
+
+  // loader result is cacheable
+  this.cacheable();
+
+  // webpack 1: prefer loader query, else options object
+  // webpack 2: prefer loader options
+  // webpack 3: deprecate loader.options object
+  // webpack 4: loader.options no longer defined
+  var options = Object.assign(
+    {},
+    this.options && this.options.adjustSourcemapLoader,
+    loaderUtils.getOptions(this),
+    {sep: path.sep}
+  );
+
+  // process the source-map
+  var outputMap = process(this, options, sourceMap);
+
+  // need to use callback when there are multiple arguments
+  this.callback(null, content, outputMap);
+}
+
+module.exports = loader;