📦 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/codec/source-relative.js

@@ -0,0 +1,51 @@
+'use strict';
+
+var path = require('path'),
+    fs   = require('fs');
+
+/**
+ * Codec for relative paths with respect to the source directory.
+ * @type {{name:string, decode: function, encode: function, root: function}}
+ */
+module.exports = {
+  name  : 'sourceRelative',
+  decode: decode,
+  encode: encode,
+  root  : root
+};
+
+/**
+ * Decode the given uri.
+ * Any path without leading slash is tested against source directory.
+ * @this {{options: object}} A loader or compilation
+ * @param {string} uri A source uri to decode
+ * @returns {boolean|string} False where unmatched else the decoded path
+ */
+function decode(uri) {
+  /* jshint validthis:true */
+  var base    = !uri.startsWith('/') && this.context,
+      absFile = !!base && path.normalize(path.join(base, uri)),
+      isValid = !!absFile && fs.existsSync(absFile) && fs.statSync(absFile).isFile();
+  return isValid && absFile;
+}
+
+/**
+ * Encode the given file path.
+ * @this {{options: object}} A loader or compilation
+ * @param {string} absolute An absolute file path to encode
+ * @returns {string} A uri without leading slash
+ */
+function encode(absolute) {
+  /* jshint validthis:true */
+  return path.relative(this.context, absolute);
+}
+
+/**
+ * The source-map root where relevant.
+ * @this {{options: object}} A loader or compilation
+ * @returns {string|undefined} The source-map root applicable to any encoded uri
+ */
+function root() {
+  /* jshint validthis:true */
+  return this.context;
+}