perf(streaming): quiesce retired generations and budget teardown

Publish the retail blocking-for-cells edge before deferred recenter work, freeze old-world presentation/simulation/audio, and advance full-window retirement from exact metered entity and owner cursors. This removes synchronous portal teardown without allowing retained owners to remain observable.

src/AcDream.App/Streaming/StreamingCompletionQueue.cs

@@ -167,6 +167,21 @@ internal sealed class StreamingCompletionQueue
         _retainedCpuBytes = 0;
     }
 
+    public bool TryRemoveOne()
+    {
+        for (int priority = 0; priority < _queues.Length; priority++)
+        {
+            Queue<StreamingQueuedCompletion> queue = _queues[priority];
+            if (!queue.TryDequeue(out StreamingQueuedCompletion completion))
+                continue;
+
+            Release(completion);
+            return true;
+        }
+
+        return false;
+    }
+
     public StreamingCompletionQueueSnapshot CaptureSnapshot()
     {
         long now = Stopwatch.GetTimestamp();