perf(renderer): coalesce status-change UI updates into one rAF frame

Non-uploading progress events (queued/getting-server/retrying/done/
error/aborted/skipped) were firing renderQueueTable +
updateQueueActionButtons + updateStatusBar + updateStatsPanel
synchronously on EVERY event. At batch start, 500 jobs going
preview→queued→getting-server within milliseconds meant ~2000 sync DOM
updates — visible jank on large batches.

New scheduleStatusChangeUpdate() uses requestAnimationFrame to coalesce
the four-helper call into at most one run per frame (~60 Hz). Functional
result is identical; the user just sees smooth flips instead of a
briefly frozen renderer.

The uploading-progress throttle (200ms) is unchanged since those events
are much more frequent and the user doesn't need 60 Hz upload-byte
updates.

renderer/app.js

@@ -918,6 +918,23 @@ function scheduleThrottledUIUpdate() {
   }, UI_UPDATE_INTERVAL);
 }
 
+// Coalesces status-change updates (done/error/retrying/queued/…) into one
+// frame. Without this, a batch of 500 jobs flipping queued→getting-server
+// →uploading synchronously fires 1500+ updateStatusBar/Buttons/Stats calls
+// and janks the renderer. rAF caps it to ~60 Hz.
+let _statusChangeUpdateQueued = false;
+function scheduleStatusChangeUpdate() {
+  if (_statusChangeUpdateQueued) return;
+  _statusChangeUpdateQueued = true;
+  requestAnimationFrame(() => {
+    _statusChangeUpdateQueued = false;
+    renderQueueTable();
+    updateQueueActionButtons();
+    updateStatusBar();
+    updateStatsPanel();
+  });
+}
+
 function buildRowHtml(job) {
   const statusClass = `status-${job.status}`;
   const rowClass = `queue-row ${statusClass}${selectedJobIds.has(job.id) ? ' selected' : ''}`;
@@ -1859,14 +1876,13 @@ function handleProgress(data) {
     queueJobs = queueJobs.filter(j => j !== job);
   }
 
-  // Status changes (done/error/etc) get immediate render; ongoing progress is throttled
+  // Status changes (done/error/etc) get one coalesced update per frame so a
+  // burst of 500 parallel jobs flipping state doesn't fire 2000 sync DOM
+  // updates. Ongoing uploading progress is throttled at 200ms.
   if (data.status === 'uploading') {
     scheduleThrottledUIUpdate();
   } else {
-    scheduleQueueRender();
+    scheduleStatusChangeUpdate();
-    updateQueueActionButtons();
-    updateStatusBar();
-    updateStatsPanel();
   }
   persistQueueStateSoon();
 }