📦 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/process/throw-errors.js

@@ -0,0 +1,30 @@
+'use strict';
+
+var getError = require('./get-error');
+
+/**
+ * Where the given list is non-null and contains error instances then consolidate and throw
+ * @throws Error
+ * @param {string} resourcePath The path to the resource being processed
+ * @param {null|Array} candidates A possible Array with possible error elements
+ */
+function throwErrors(resourcePath, candidates) {
+  var errors = !!candidates && candidates
+      .filter(testIsError)
+      .map(getMessage);
+
+  var hasError = !!errors && errors.length;
+  if (hasError) {
+    throw getError(['For resource: ' + resourcePath].concat(errors).join('\n'));
+  }
+
+  function testIsError(candidate) {
+    return !!candidate && (typeof candidate === 'object') && (candidate instanceof Error);
+  }
+
+  function getMessage(error) {
+    return error.message;
+  }
+}
+
+module.exports = throwErrors;