feat(seo): return a real 404 status for unmatched routes

src/app.js

@@ -270,7 +270,7 @@ export function createApp(config, prisma) {
     })
   );
   app.get(/^\/(?!api\/).*/, (req, res) => {
-    res.sendFile(path.join(frontendDist, 'index.html'));
+    res.status(404).sendFile(path.join(frontendDist, '404', 'index.html'));
   });
 
   app.use((err, req, res, next) => {