feat(client): 添加 Node.js 客户端及示例应用

- 新增 nodejs-client 模块，提供 ConfigClient 配置拉取、定时同步、变更监听
- 使用 Node.js 内置 crypto 模块实现 AES 解密，零外部依赖
- 新增 nodejs-client-demo Express 示例应用，端口 8083
- 更新 README.md，补充 Python 和 Node.js 客户端使用说明
- 修复 fetchAllConfigs API 响应格式判断逻辑

nodejs-client/README.md

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+# Kenaito Config Center Node.js Client
+
+## 安装
+
+### 安装到本地仓库（推荐）
+
+将包注册为全局符号链接，之后任意项目都可以通过 `npm link kenaito-conf` 引用：
+
+```bash
+cd nodejs-client
+npm link
+```
+
+在你的项目中使用：
+
+```bash
+npm link kenaito-conf
+```
+
+### 直接引用
+
+```bash
+# 在你的项目 package.json 中
+"dependencies": {
+  "kenaito-conf": "file:../nodejs-client"
+}
+```
+
+```bash
+npm install
+```
+
+## 快速开始
+
+```javascript
+import { Config, ConfigClient } from 'kenaito-conf';
+
+const config = new Config({
+  baseUrl: 'http://localhost:8080',
+  appName: 'my-app',
+  env: 'daily',
+  syncInterval: 30,
+});
+
+const client = new ConfigClient(config);
+
+// 监听配置变更
+client.onChange((changed) => {
+  for (const [k, v] of Object.entries(changed)) {
+    console.log(`config changed: ${k} = ${v}`);
+  }
+});
+
+// 启动客户端（拉取配置 + 开启定时同步）
+await client.start();
+
+// 获取配置
+const value = client.get('database.host');
+const allConfigs = client.getAll();
+
+// 停止
+client.stop();
+```
+
+## 配置项
+
+| 参数 | 说明 | 默认值 |
+|------|------|--------|
+| `baseUrl` | 配置中心地址 | 必填 |
+| `appName` | 应用名称 | 必填 |
+| `env` | 环境（dev/daily/prod） | `dev` |
+| `version` | 配置版本 | `latest` |
+| `token` | 认证令牌 | 空 |
+| `syncInterval` | 同步间隔（秒） | `60` |
+| `ignoreGlobal` | 是否忽略全局配置 | `false` |
+| `cacheDir` | 本地缓存目录 | `.` |
+
+## Demo
+
+```bash
+cd nodejs-client-demo
+npm install
+node app.js
+```
+
+Demo 默认监听 `8083` 端口，访问 `http://localhost:8083/` 查看配置。
+
+环境变量覆盖：
+
+| 环境变量 | 说明 | 默认值 |
+|----------|------|--------|
+| `SERVER_PORT` | 服务端口 | `8083` |
+| `KENAITO_BASE_URL` | 配置中心地址 | `http://localhost:8080` |
+| `KENAITO_APP_NAME` | 应用名称 | `kenaito-nodejs-demo` |
+| `KENAITO_PROFILE` | 环境 | `daily` |
+| `KENAITO_VERSION` | 配置版本 | `latest` |
+| `KENAITO_TOKEN` | 认证令牌 | 空 |
+| `KENAITO_SYNC_INTERVAL` | 同步间隔（秒） | `30` |
+| `KENAITO_CACHE_DIR` | 缓存目录 | `.` |

nodejs-client/lib/cache.js

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+import fs from 'node:fs';
+import path from 'node:path';
+
+const CACHE_FILE = 'config-cache.json';
+
+export class Cache {
+  constructor(cacheDir = '.') {
+    this.cacheDir = cacheDir;
+  }
+
+  write(data) {
+    const filePath = path.join(this.cacheDir, CACHE_FILE);
+    fs.writeFileSync(filePath, JSON.stringify(data, null, 2), 'utf8');
+  }
+
+  read() {
+    const filePath = path.join(this.cacheDir, CACHE_FILE);
+    try {
+      const content = fs.readFileSync(filePath, 'utf8');
+      return JSON.parse(content);
+    } catch {
+      return null;
+    }
+  }
+}

nodejs-client/lib/client.js

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+import { Config } from './config.js';
+import { Cache } from './cache.js';
+import { Listener } from './listener.js';
+import { decryptConfig } from './crypto.js';
+
+export class ConfigClient {
+  constructor(config) {
+    this.config = config;
+    this.cache = new Cache(config.cacheDir);
+    this.listener = new Listener();
+    this.configs = {};
+    this.secret = '';
+    this.globalSecret = '';
+    this.lastTime = 0;
+    this.started = false;
+    this.timer = null;
+  }
+
+  onChange(handler) {
+    this.listener.onChange(handler);
+  }
+
+  get(key) {
+    return this.configs[key] ?? null;
+  }
+
+  getAll() {
+    return { ...this.configs };
+  }
+
+  async start() {
+    if (this.started) {
+      return;
+    }
+    this.started = true;
+
+    try {
+      await this.fetchAll();
+    } catch (err) {
+      console.warn('[ConfigClient] fetch all configs error:', err.message, ', trying cache');
+      const cached = this.cache.read();
+      if (cached) {
+        this.applyConfigs(cached);
+        console.info('[ConfigClient] loaded', Object.keys(this.configs).length, 'configs from cache');
+      } else {
+        throw new Error(`fetch configs failed and no cache: ${err.message}`);
+      }
+    }
+
+    this.timer = setInterval(() => {
+      this.fetchChanged().catch((err) => {
+        console.error('[ConfigClient] sync error:', err);
+      });
+    }, this.config.syncInterval * 1000);
+  }
+
+  stop() {
+    if (this.timer) {
+      clearInterval(this.timer);
+      this.timer = null;
+    }
+  }
+
+  async fetchAll() {
+    const url = `${this.config.baseUrl}/api/fetchAllConfigs?appName=${encodeURIComponent(this.config.appName)}&env=${encodeURIComponent(this.config.env)}&version=${encodeURIComponent(this.config.version)}&ignoreGlobal=${this.config.ignoreGlobal}`;
+    const resp = await fetch(url, {
+      headers: this.config.token ? { Authorization: `Bearer ${this.config.token}` } : {},
+      signal: AbortSignal.timeout(10000),
+    });
+    if (!resp.ok) {
+      throw new Error(`HTTP ${resp.status}`);
+    }
+    const data = await resp.json();
+    if (data.code != null && data.code !== 0) {
+      throw new Error(`server error: ${data.msg || 'unknown'}`);
+    }
+
+    const secret = data['kenaito.config.encrypt-secret'];
+    if (secret) {
+      this.secret = secret;
+    }
+    const globalSecret = data['kenaito.config.global-encrypt-secret'];
+    if (globalSecret) {
+      this.globalSecret = globalSecret;
+    }
+    const ts = data['latest.fetch.timestamp'];
+    if (ts) {
+      this.lastTime = parseInt(ts, 10);
+    }
+
+    this.cache.write(data);
+    this.applyConfigs(data);
+    console.info('[ConfigClient] fetched', Object.keys(this.configs).length, 'configs');
+  }
+
+  async fetchChanged() {
+    const url = `${this.config.baseUrl}/api/fetchChangedConfigs`;
+    const payload = {
+      appName: this.config.appName,
+      env: this.config.env,
+      version: this.config.version,
+      lastTime: this.lastTime,
+      ignoreGlobal: this.config.ignoreGlobal,
+    };
+    const resp = await fetch(url, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        ...(this.config.token ? { Authorization: `Bearer ${this.config.token}` } : {}),
+      },
+      body: JSON.stringify(payload),
+      signal: AbortSignal.timeout(10000),
+    });
+    if (!resp.ok) {
+      throw new Error(`HTTP ${resp.status}`);
+    }
+    const result = await resp.json();
+    if (result.code !== 0) {
+      throw new Error(`server error code: ${result.code}`);
+    }
+
+    const changedData = result.data || {};
+    const ts = changedData['latest.fetch.timestamp'];
+    if (ts) {
+      this.lastTime = parseInt(ts, 10);
+    }
+    delete changedData['latest.fetch.timestamp'];
+
+    const changed = {};
+    for (const [k, v] of Object.entries(changedData)) {
+      changed[k] = this.tryDecrypt(v);
+    }
+
+    Object.assign(this.configs, changed);
+    this.listener.notify(changed);
+    console.info('[ConfigClient]', Object.keys(changed).length, 'configs changed');
+  }
+
+  applyConfigs(data) {
+    for (const [k, v] of Object.entries(data)) {
+      if (k.startsWith('kenaito.') || k === 'latest.fetch.timestamp') {
+        continue;
+      }
+      if (typeof v !== 'string') {
+        continue;
+      }
+      this.configs[k] = this.tryDecrypt(v);
+    }
+  }
+
+  tryDecrypt(value) {
+    let decrypted = decryptConfig(this.secret, value);
+    if (decrypted === value && this.globalSecret) {
+      decrypted = decryptConfig(this.globalSecret, value);
+    }
+    return decrypted;
+  }
+}
+
+export { Config } from './config.js';

nodejs-client/lib/config.js

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+export class Config {
+  constructor(options = {}) {
+    this.baseUrl = options.baseUrl || '';
+    this.appName = options.appName || '';
+    this.env = options.env || 'dev';
+    this.version = options.version || 'latest';
+    this.token = options.token || '';
+    this.syncInterval = options.syncInterval || 60;
+    this.ignoreGlobal = options.ignoreGlobal || false;
+    this.cacheDir = options.cacheDir || '.';
+  }
+}

nodejs-client/lib/crypto.js

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+import crypto from 'node:crypto';
+
+const CRYPT_PREFIX = '{Cipher}';
+
+export function decryptConfig(secret, data) {
+  if (!data.startsWith(CRYPT_PREFIX)) {
+    return data;
+  }
+  const encrypted = data.slice(CRYPT_PREFIX.length);
+  return decryptWithAES(secret, encrypted);
+}
+
+export function decryptWithAES(key, data) {
+  const md5Hash = crypto.createHash('md5').update(key).digest('hex');
+  const aesKey = md5Hash.slice(16);
+  const cipherText = Buffer.from(data, 'base64');
+  const iv = Buffer.alloc(16, 0);
+  const decipher = crypto.createDecipheriv('aes-128-cbc', aesKey, iv);
+  decipher.setAutoPadding(false);
+  let plainText = Buffer.concat([decipher.update(cipherText), decipher.final()]);
+  const padding = plainText[plainText.length - 1];
+  plainText = plainText.slice(0, plainText.length - padding);
+  return plainText.toString('utf8');
+}

nodejs-client/lib/index.js

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+export { ConfigClient, Config } from './client.js';

nodejs-client/lib/listener.js

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+export class Listener {
+  constructor() {
+    this.handlers = [];
+  }
+
+  onChange(handler) {
+    this.handlers.push(handler);
+  }
+
+  notify(changed) {
+    for (const handler of this.handlers) {
+      try {
+        handler(changed);
+      } catch (err) {
+        console.error('[ConfigClient] change handler error:', err);
+      }
+    }
+  }
+}

nodejs-client/package.json

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+{
+  "name": "kenaito-conf",
+  "version": "1.0.0",
+  "description": "Kenaito Config Center Node.js Client",
+  "type": "module",
+  "main": "lib/index.js",
+  "exports": {
+    ".": "./lib/index.js"
+  },
+  "engines": {
+    "node": ">=18.0.0"
+  },
+  "keywords": [
+    "config",
+    "configuration",
+    "config-center"
+  ],
+  "author": "odboy",
+  "license": "MIT"
+}