core: use common plugin-api interface

packages/hydrooj/package.json

@@ -2,8 +2,8 @@
     "name": "hydrooj",
     "version": "3.17.12",
     "bin": "bin/hydrooj.js",
-    "main": "src/loader",
-    "module": "src/loader",
+    "main": "src/plugin-api",
+    "module": "src/plugin-api",
     "repository": "https://github.com/hydro-dev/Hydro.git",
     "author": "undefined <i@undefined.moe>",
     "license": "AGPL-3.0-or-later",