📦 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/ajv/lib/refs/data.json

@@ -0,0 +1,17 @@
+{
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "$id": "https://raw.githubusercontent.com/ajv-validator/ajv/master/lib/refs/data.json#",
+    "description": "Meta-schema for $data reference (JSON Schema extension proposal)",
+    "type": "object",
+    "required": [ "$data" ],
+    "properties": {
+        "$data": {
+            "type": "string",
+            "anyOf": [
+                { "format": "relative-json-pointer" }, 
+                { "format": "json-pointer" }
+            ]
+        }
+    },
+    "additionalProperties": false
+}