📦 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/_baseClamp.js

@@ -0,0 +1,22 @@
+/**
+ * The base implementation of `_.clamp` which doesn't coerce arguments.
+ *
+ * @private
+ * @param {number} number The number to clamp.
+ * @param {number} [lower] The lower bound.
+ * @param {number} upper The upper bound.
+ * @returns {number} Returns the clamped number.
+ */
+function baseClamp(number, lower, upper) {
+  if (number === number) {
+    if (upper !== undefined) {
+      number = number <= upper ? number : upper;
+    }
+    if (lower !== undefined) {
+      number = number >= lower ? number : lower;
+    }
+  }
+  return number;
+}
+
+module.exports = baseClamp;