refactor: Express 제거, 순수 Node.js http 모듈로 교체

- server.js: http 모듈만 사용, 정적 파일 서빙 + API 3개
- package.json: dependencies 제거 (외부 패키지 없음)
- package-lock.json 삭제

server.js

@@ -1,45 +1,86 @@
-const express = require('express');
+const http = require('http');
+const fs = require('fs');
 const path = require('path');
 
-const app = express();
 const PORT = process.env.PORT || 3000;
+const PUBLIC_DIR = path.join(__dirname, 'public');
 
-app.use(express.json());
-app.use(express.static(path.join(__dirname, 'public')));
+const MIME_TYPES = {
+  '.html': 'text/html; charset=utf-8',
+  '.css':  'text/css',
+  '.js':   'text/javascript',
+  '.png':  'image/png',
+  '.jpg':  'image/jpeg',
+  '.ico':  'image/x-icon',
+};
 
-// API routes
-app.get('/api/greeting', (req, res) => {
-  const greetings = [
-    '안녕하세요! 👋',
-    '반갑습니다! 😊',
-    '어서오세요! 🌸',
-    '좋은 하루예요! ☀️',
-    '환영합니다! 🎉',
-  ];
-  const message = greetings[Math.floor(Math.random() * greetings.length)];
-  res.json({ message });
-});
-
-app.get('/api/stats', (req, res) => {
-  res.json({
-    uptime: Math.floor(process.uptime()),
-    nodeVersion: process.version,
-    platform: process.platform,
-    deployedAt: new Date().toISOString(),
+function serveStatic(res, filePath) {
+  fs.readFile(filePath, (err, data) => {
+    if (err) {
+      res.writeHead(404);
+      res.end('Not Found');
+      return;
+    }
+    const ext = path.extname(filePath);
+    res.writeHead(200, { 'Content-Type': MIME_TYPES[ext] || 'application/octet-stream' });
+    res.end(data);
   });
+}
+
+function sendJson(res, status, body) {
+  res.writeHead(status, { 'Content-Type': 'application/json' });
+  res.end(JSON.stringify(body));
+}
+
+function readBody(req) {
+  return new Promise((resolve) => {
+    let body = '';
+    req.on('data', chunk => { body += chunk; });
+    req.on('end', () => {
+      try { resolve(JSON.parse(body)); }
+      catch { resolve({}); }
+    });
+  });
+}
+
+const server = http.createServer(async (req, res) => {
+  const url = new URL(req.url, `http://localhost`);
+  const pathname = url.pathname;
+
+  // API routes
+  if (pathname === '/api/greeting' && req.method === 'GET') {
+    const greetings = ['안녕하세요! 👋', '반갑습니다! 😊', '어서오세요! 🌸', '좋은 하루예요! ☀️', '환영합니다! 🎉'];
+    sendJson(res, 200, { message: greetings[Math.floor(Math.random() * greetings.length)] });
+    return;
+  }
+
+  if (pathname === '/api/stats' && req.method === 'GET') {
+    sendJson(res, 200, {
+      uptime: Math.floor(process.uptime()),
+      nodeVersion: process.version,
+      platform: process.platform,
+      deployedAt: new Date().toISOString(),
+    });
+    return;
+  }
+
+  if (pathname === '/api/echo' && req.method === 'POST') {
+    const { text } = await readBody(req);
+    if (!text) { sendJson(res, 400, { error: '텍스트를 입력해주세요.' }); return; }
+    sendJson(res, 200, { echo: text, length: text.length });
+    return;
+  }
+
+  // Static files
+  const filePath = path.join(PUBLIC_DIR, pathname === '/' ? 'index.html' : pathname);
+  const ext = path.extname(filePath);
+  if (ext) {
+    serveStatic(res, filePath);
+  } else {
+    serveStatic(res, path.join(PUBLIC_DIR, 'index.html'));
+  }
 });
 
-app.post('/api/echo', (req, res) => {
-  const { text } = req.body;
-  if (!text) return res.status(400).json({ error: '텍스트를 입력해주세요.' });
-  res.json({ echo: text, length: text.length });
-});
-
-// Fallback to index.html for unknown routes
-app.get('*', (req, res) => {
-  res.sendFile(path.join(__dirname, 'public', 'index.html'));
-});
-
-app.listen(PORT, () => {
+server.listen(PORT, () => {
   console.log(`서버 실행 중: http://localhost:${PORT}`);
 });