perf: background poller for near-instant dashboard responses

- New poller.js polls all services on a configurable interval
- POLL_INTERVAL env var (default 5000ms / 5 seconds)
- All data stored in cache with TTL of 3x poll interval
- Dashboard endpoint now reads from cache only (no network calls)
- API responses are near-instant regardless of service count
- First poll runs immediately on server start

server/index.js

@@ -54,6 +54,7 @@ const radarrRoutes = require('./routes/radarr');
 const embyRoutes = require('./routes/emby');
 const dashboardRoutes = require('./routes/dashboard');
 const authRoutes = require('./routes/auth');
+const { startPoller, POLL_INTERVAL } = require('./utils/poller');
 
 const app = express();
 const PORT = process.env.PORT || 3001;
@@ -79,5 +80,7 @@ app.listen(PORT, () => {
   console.log(`  sofarr - Your Downloads Dashboard`);
   console.log(`  Server running on port ${PORT}`);
   console.log(`  Log level: ${process.env.LOG_LEVEL || 'info'}`);
+  console.log(`  Poll interval: ${POLL_INTERVAL}ms`);
   console.log(`=================================`);
+  startPoller();
 });