Convert backend to ESM

- About 5 years overdue
- Remove eslint, use bomejs instead

backend/lib/express/user-id-from-me.js

@@ -1,9 +1,8 @@
-module.exports = (req, res, next) => {
+export default (req, res, next) => {
 	if (req.params.user_id === 'me' && res.locals.access) {
 		req.params.user_id = res.locals.access.token.get('attrs').id;
 	} else {
-		req.params.user_id = parseInt(req.params.user_id, 10);
+		req.params.user_id = Number.parseInt(req.params.user_id, 10);
 	}
-
 	next();
 };