📦 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/lodash/isArrayBuffer.js

@@ -0,0 +1,27 @@
+var baseIsArrayBuffer = require('./_baseIsArrayBuffer'),
+    baseUnary = require('./_baseUnary'),
+    nodeUtil = require('./_nodeUtil');
+
+/* Node.js helper references. */
+var nodeIsArrayBuffer = nodeUtil && nodeUtil.isArrayBuffer;
+
+/**
+ * Checks if `value` is classified as an `ArrayBuffer` object.
+ *
+ * @static
+ * @memberOf _
+ * @since 4.3.0
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is an array buffer, else `false`.
+ * @example
+ *
+ * _.isArrayBuffer(new ArrayBuffer(2));
+ * // => true
+ *
+ * _.isArrayBuffer(new Array(2));
+ * // => false
+ */
+var isArrayBuffer = nodeIsArrayBuffer ? baseUnary(nodeIsArrayBuffer) : baseIsArrayBuffer;
+
+module.exports = isArrayBuffer;