📦 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/eslint-plugin-jsx-a11y/lib/util/getExplicitRole.js

@@ -0,0 +1,27 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports["default"] = getExplicitRole;
+var _ariaQuery = require("aria-query");
+var _jsxAstUtils = require("jsx-ast-utils");
+/**
+ * Returns an element's computed role, which is
+ *
+ *  1. The valid value of its explicit role attribute; or
+ *  2. The implicit value of its tag.
+ */
+function getExplicitRole(tag, attributes) {
+  var explicitRole = function toLowerCase(role) {
+    if (typeof role === 'string') {
+      return role.toLowerCase();
+    }
+    return null;
+  }((0, _jsxAstUtils.getLiteralPropValue)((0, _jsxAstUtils.getProp)(attributes, 'role')));
+  if (_ariaQuery.roles.has(explicitRole)) {
+    return explicitRole;
+  }
+  return null;
+}
+module.exports = exports.default;