📦 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/definition_schema.js

@@ -0,0 +1,37 @@
+'use strict';
+
+var metaSchema = require('./refs/json-schema-draft-07.json');
+
+module.exports = {
+  $id: 'https://github.com/ajv-validator/ajv/blob/master/lib/definition_schema.js',
+  definitions: {
+    simpleTypes: metaSchema.definitions.simpleTypes
+  },
+  type: 'object',
+  dependencies: {
+    schema: ['validate'],
+    $data: ['validate'],
+    statements: ['inline'],
+    valid: {not: {required: ['macro']}}
+  },
+  properties: {
+    type: metaSchema.properties.type,
+    schema: {type: 'boolean'},
+    statements: {type: 'boolean'},
+    dependencies: {
+      type: 'array',
+      items: {type: 'string'}
+    },
+    metaSchema: {type: 'object'},
+    modifying: {type: 'boolean'},
+    valid: {type: 'boolean'},
+    $data: {type: 'boolean'},
+    async: {type: 'boolean'},
+    errors: {
+      anyOf: [
+        {type: 'boolean'},
+        {const: 'full'}
+      ]
+    }
+  }
+};