fix(web): localStorage safety, default fetch timeout, visibility-aware polling

web/src/composables/useNotifications.ts

@@ -18,13 +18,35 @@ export function useUnreadPoller() {
     }
   }
 
-  onMounted(() => {
+  function start() {
+    if (timer !== null) return
     refresh()
     timer = setInterval(refresh, POLL_INTERVAL_MS)
+  }
+
+  function stop() {
+    if (timer !== null) {
+      clearInterval(timer)
+      timer = null
+    }
+  }
+
+  function onVisibilityChange() {
+    if (document.hidden) {
+      stop()
+    } else {
+      start()
+    }
+  }
+
+  onMounted(() => {
+    start()
+    document.addEventListener('visibilitychange', onVisibilityChange)
   })
 
   onUnmounted(() => {
-    if (timer) clearInterval(timer)
+    document.removeEventListener('visibilitychange', onVisibilityChange)
+    stop()
   })
 
   return { refresh, error }