📦 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/_baseAggregator.js

@@ -0,0 +1,21 @@
+var baseEach = require('./_baseEach');
+
+/**
+ * Aggregates elements of `collection` on `accumulator` with keys transformed
+ * by `iteratee` and values set by `setter`.
+ *
+ * @private
+ * @param {Array|Object} collection The collection to iterate over.
+ * @param {Function} setter The function to set `accumulator` values.
+ * @param {Function} iteratee The iteratee to transform keys.
+ * @param {Object} accumulator The initial aggregated object.
+ * @returns {Function} Returns `accumulator`.
+ */
+function baseAggregator(collection, setter, iteratee, accumulator) {
+  baseEach(collection, function(value, key, collection) {
+    setter(accumulator, value, iteratee(value), collection);
+  });
+  return accumulator;
+}
+
+module.exports = baseAggregator;