📦 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/array-flatten/array-flatten.js

@@ -0,0 +1,64 @@
+'use strict'
+
+/**
+ * Expose `arrayFlatten`.
+ */
+module.exports = arrayFlatten
+
+/**
+ * Recursive flatten function with depth.
+ *
+ * @param  {Array}  array
+ * @param  {Array}  result
+ * @param  {Number} depth
+ * @return {Array}
+ */
+function flattenWithDepth (array, result, depth) {
+  for (var i = 0; i < array.length; i++) {
+    var value = array[i]
+
+    if (depth > 0 && Array.isArray(value)) {
+      flattenWithDepth(value, result, depth - 1)
+    } else {
+      result.push(value)
+    }
+  }
+
+  return result
+}
+
+/**
+ * Recursive flatten function. Omitting depth is slightly faster.
+ *
+ * @param  {Array} array
+ * @param  {Array} result
+ * @return {Array}
+ */
+function flattenForever (array, result) {
+  for (var i = 0; i < array.length; i++) {
+    var value = array[i]
+
+    if (Array.isArray(value)) {
+      flattenForever(value, result)
+    } else {
+      result.push(value)
+    }
+  }
+
+  return result
+}
+
+/**
+ * Flatten an array, with the ability to define a depth.
+ *
+ * @param  {Array}  array
+ * @param  {Number} depth
+ * @return {Array}
+ */
+function arrayFlatten (array, depth) {
+  if (depth == null) {
+    return flattenForever(array, [])
+  }
+
+  return flattenWithDepth(array, [], depth)
+}