📦 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/omitBy.js

@@ -0,0 +1,29 @@
+var baseIteratee = require('./_baseIteratee'),
+    negate = require('./negate'),
+    pickBy = require('./pickBy');
+
+/**
+ * The opposite of `_.pickBy`; this method creates an object composed of
+ * the own and inherited enumerable string keyed properties of `object` that
+ * `predicate` doesn't return truthy for. The predicate is invoked with two
+ * arguments: (value, key).
+ *
+ * @static
+ * @memberOf _
+ * @since 4.0.0
+ * @category Object
+ * @param {Object} object The source object.
+ * @param {Function} [predicate=_.identity] The function invoked per property.
+ * @returns {Object} Returns the new object.
+ * @example
+ *
+ * var object = { 'a': 1, 'b': '2', 'c': 3 };
+ *
+ * _.omitBy(object, _.isNumber);
+ * // => { 'b': '2' }
+ */
+function omitBy(object, predicate) {
+  return pickBy(object, negate(baseIteratee(predicate)));
+}
+
+module.exports = omitBy;