docs: 添加 NestJS 后端 API 完整文档

- 新增中英文 NestJS API 用户指南 (api-nestjs.md)
- 包含 12 个模块 60 个端点的完整 API 参考
- 每个端点包含请求/响应示例和 curl 命令
- 添加 JWT 认证流程和错误处理指南
- 更新 sidebar 配置添加 NestJS API 导航

Author: h7ml

.vitepress/sidebar.ts

@@ -36,6 +36,7 @@ const zhGuideSidebar: DefaultTheme.SidebarItem[] = [
       { text: '🦕 Deno + Hono', link: '/guide/deno' },
       { text: '🐹 Go API', link: '/guide/api-go' },
       { text: '🟩 Node.js API', link: '/guide/api-node' },
+      { text: '🏗️ NestJS API', link: '/guide/api-nestjs' },
       { text: '🐍 Python FastAPI', link: '/guide/api-python' },
       { text: '☕ Java Spring Boot', link: '/guide/api-java' },
       { text: '🍞 Bun + Hono', link: '/guide/api-bun' },
@@ -115,6 +116,7 @@ const enGuideSidebar: DefaultTheme.SidebarItem[] = [
       { text: '🦕 Deno + Hono', link: '/en/guide/deno' },
       { text: '🐹 Go API', link: '/en/guide/api-go' },
       { text: '🟩 Node.js API', link: '/en/guide/api-node' },
+      { text: '🏗️ NestJS API', link: '/en/guide/api-nestjs' },
       { text: '🐍 Python FastAPI', link: '/en/guide/api-python' },
       { text: '☕ Java Spring Boot', link: '/en/guide/api-java' },
       { text: '🍞 Bun + Hono', link: '/en/guide/api-bun' },