make fallback middleware which responds with 404 not found

backend/src/index.js

@@ -47,6 +47,10 @@ app.use(express.static(path.join(__dirname, "public"), {
 app.use("/api/docs", swaggerUi.serve, swaggerUi.setup(specs));
 app.use("/api", apiRouter);
 
+app.use((req, res) => {
+  res.status(404).send("Not Found");
+})
+
 // has to be last
 app.use((_req, res, _next) => {
   const err = res.error;