📦 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/jsonpath/test/data/store.json

@@ -0,0 +1,31 @@
+{ "store": {
+    "book": [ 
+      { "category": "reference",
+        "author": "Nigel Rees",
+        "title": "Sayings of the Century",
+        "price": 8.95
+      },
+      { "category": "fiction",
+        "author": "Evelyn Waugh",
+        "title": "Sword of Honour",
+        "price": 12.99
+      },
+      { "category": "fiction",
+        "author": "Herman Melville",
+        "title": "Moby Dick",
+        "isbn": "0-553-21311-3",
+        "price": 8.99
+      },
+      { "category": "fiction",
+        "author": "J. R. R. Tolkien",
+        "title": "The Lord of the Rings",
+        "isbn": "0-395-19395-8",
+        "price": 22.99
+      }
+    ],
+    "bicycle": {
+      "color": "red",
+      "price": 19.95
+    }
+  }
+}