add linter to backend and change workflow

.github/workflows/pipeline.yml

@@ -16,6 +16,8 @@ jobs:
       #   - uses: superfly/flyctl-actions/setup-flyctl@master
       - name: Install dependencies for backend
         run: npm ci
+      - name: Lint backend
+        run: npm run lint:backend
       - name: Test backend
         run: npm run test:backend
       - name: Install dependencies for frontend

eslint.config.mjs

@@ -0,0 +1,9 @@
+import globals from "globals";
+import pluginJs from "@eslint/js";
+
+
+export default [
+  {files: ["**/*.js"], languageOptions: {sourceType: "commonjs"}},
+  {languageOptions: { globals: globals.node }},
+  pluginJs.configs.recommended,
+];