📦 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/getComputedRole.js

@@ -0,0 +1,19 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports["default"] = getComputedRole;
+var _getExplicitRole = _interopRequireDefault(require("./getExplicitRole"));
+var _getImplicitRole = _interopRequireDefault(require("./getImplicitRole"));
+function _interopRequireDefault(e) { return e && e.__esModule ? e : { "default": e }; }
+/**
+ * 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 getComputedRole(tag, attributes) {
+  return (0, _getExplicitRole["default"])(tag, attributes) || (0, _getImplicitRole["default"])(tag, attributes);
+}
+module.exports = exports.default;