fix: convert kordoc service to ESM (kordoc requires ESM import)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

services/kordoc/server.js

@@ -2,10 +2,10 @@
  * kordoc 마이크로서비스 — HWP/HWPX/PDF/텍스트 → Markdown 변환 API
  */
 
-const express = require('express');
-const fs = require('fs');
-const path = require('path');
-const { parse, detectFormat } = require('kordoc');
+import express from 'express';
+import fs from 'fs';
+import path from 'path';
+import { parse, detectFormat } from 'kordoc';
 
 const app = express();
 const PORT = 3100;