add basic backend code

package.json

@@ -1,7 +1,7 @@
 {
   "name": "zhdiary",
   "version": "1.0.0",
-  "main": "index.js",
+  "private": true,
   "repository": "https://github.com/patarapolw/zhdiary.git",
   "author": "Pacharapol Withayasakpunt <patarapolw@gmail.com> (https://polvcode.dev)",
   "license": "MIT",