feat: periodically re-poll queue progress state (#9136)

## Summary
- Add `useQueuePolling` composable that polls `queueStore.update()`
every 5s while jobs are active
- Calls `update()` immediately on creation so the UI is current after
page reload
- Uses `useIntervalFn` + `watch` pattern (same as `assetDownloadStore`)
to pause/resume based on `activeJobsCount`

## Related Issue
- Related to #8136

## QA
- Queue a prompt, reload page mid-execution, verify queue UI updates
every ~5s
- Verify polling stops when queue empties
- Verify polling resumes when new jobs are queued

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9136-feat-periodically-re-poll-queue-progress-state-3106d73d36508119a32fc5b9c8eda21c)
by [Unito](https://www.unito.io)

src/platform/remote/comfyui/useQueuePolling.ts

@@ -0,0 +1,47 @@
+import { useTimeoutFn } from '@vueuse/core'
+import { ref, watch } from 'vue'
+
+import { useQueueStore } from '@/stores/queueStore'
+
+const BASE_INTERVAL_MS = 8_000
+const MAX_INTERVAL_MS = 32_000
+const BACKOFF_MULTIPLIER = 1.5
+
+export function useQueuePolling() {
+  const queueStore = useQueueStore()
+  const delay = ref(BASE_INTERVAL_MS)
+
+  const { start, stop } = useTimeoutFn(
+    () => {
+      if (queueStore.activeJobsCount !== 1 || queueStore.isLoading) return
+      delay.value = Math.min(delay.value * BACKOFF_MULTIPLIER, MAX_INTERVAL_MS)
+      void queueStore.update()
+    },
+    delay,
+    { immediate: false }
+  )
+
+  function scheduleNextPoll() {
+    if (queueStore.activeJobsCount === 1 && !queueStore.isLoading) start()
+    else stop()
+  }
+
+  watch(
+    () => queueStore.activeJobsCount,
+    () => {
+      delay.value = BASE_INTERVAL_MS
+      scheduleNextPoll()
+    },
+    { immediate: true }
+  )
+
+  // Reschedule after any update completes (whether from polling or
+  // WebSocket events) to avoid redundant requests.
+  watch(
+    () => queueStore.isLoading,
+    (loading, wasLoading) => {
+      if (wasLoading && !loading) scheduleNextPoll()
+    },
+    { flush: 'sync' }
+  )
+}