feat: make background polling disablable with on-demand fallback

- Set POLL_INTERVAL=0, off, false, or disabled to disable background polling
- When disabled, data is fetched on-demand when a user opens the dashboard
- On-demand results cached for 30s so other users benefit from fresh data
- A user with a faster refresh rate keeps the cache warm for everyone
- When polling is enabled, behaviour is unchanged (default 5s)

server/utils/poller.js

@@ -7,7 +7,11 @@ const {
   getRadarrInstances
 } = require('./config');
 
-const POLL_INTERVAL = parseInt(process.env.POLL_INTERVAL, 10) || 5000;
+const rawPollInterval = (process.env.POLL_INTERVAL || '').toLowerCase();
+const POLL_INTERVAL = (rawPollInterval === 'off' || rawPollInterval === 'false' || rawPollInterval === 'disabled')
+  ? 0
+  : (parseInt(process.env.POLL_INTERVAL, 10) || 5000);
+const POLLING_ENABLED = POLL_INTERVAL > 0;
 
 let polling = false;
 
@@ -125,8 +129,9 @@ async function pollAllServices() {
       })
     ]);
 
-    // Aggregate and store in cache (TTL slightly longer than poll interval to avoid gaps)
-    const cacheTTL = POLL_INTERVAL * 3;
+    // When polling is active, TTL is 3x interval to avoid gaps between polls
+    // When polling is disabled (on-demand), use 30s so data refreshes on next request after expiry
+    const cacheTTL = POLLING_ENABLED ? POLL_INTERVAL * 3 : 30000;
 
     // SABnzbd
     const firstSabQueue = sabQueues[0] && sabQueues[0].data && sabQueues[0].data.queue;
@@ -182,6 +187,10 @@ async function pollAllServices() {
 let intervalHandle = null;
 
 function startPoller() {
+  if (!POLLING_ENABLED) {
+    console.log(`[Poller] Background polling disabled (POLL_INTERVAL=${process.env.POLL_INTERVAL || 'not set'}). Data will be fetched on-demand.`);
+    return;
+  }
   console.log(`[Poller] Starting background poller (interval: ${POLL_INTERVAL}ms)`);
   // Run immediately, then on interval
   pollAllServices();
@@ -196,4 +205,4 @@ function stopPoller() {
   }
 }
 
-module.exports = { startPoller, stopPoller, POLL_INTERVAL };
+module.exports = { startPoller, stopPoller, pollAllServices, POLL_INTERVAL, POLLING_ENABLED };