feat: serve built frontend and add SPA fallback for non-API routes

backend/server.js

@@ -155,6 +155,19 @@ app.delete('/api/counters/:id', async (req, res) => {
     }
 })
 
+
+// Serve built frontend (production) if it exists
+const FRONTEND_DIST = path.join(__dirname, '..', 'frontend', 'dist')
+if (fs.existsSync(FRONTEND_DIST)) {
+  app.use(express.static(FRONTEND_DIST))
+
+  // SPA fallback: serve index.html for any non-API route
+  app.get('/*path', (req, res) => {
+    if (req.path.startsWith('/api')) return res.status(404).end()
+    res.sendFile(path.join(FRONTEND_DIST, 'index.html'))
+  })
+}
+
 // graceful shutdown: ensure Prisma disconnects
 process.on('SIGINT', async () => {
   log.info('shutting down')