📦 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/eslint/lib/shared/ajv.js

@@ -0,0 +1,34 @@
+/**
+ * @fileoverview The instance of Ajv validator.
+ * @author Evgeny Poberezkin
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const Ajv = require("ajv"),
+    metaSchema = require("ajv/lib/refs/json-schema-draft-04.json");
+
+//------------------------------------------------------------------------------
+// Public Interface
+//------------------------------------------------------------------------------
+
+module.exports = (additionalOptions = {}) => {
+    const ajv = new Ajv({
+        meta: false,
+        useDefaults: true,
+        validateSchema: false,
+        missingRefs: "ignore",
+        verbose: true,
+        schemaId: "auto",
+        ...additionalOptions
+    });
+
+    ajv.addMetaSchema(metaSchema);
+    // eslint-disable-next-line no-underscore-dangle -- Ajv's API
+    ajv._opts.defaultMeta = metaSchema.id;
+
+    return ajv;
+};