[idd] capture: copy software frames directly to IVSHMEM

Bypass cadence retention when the software render adapter is active.
Publish each available source frame immediately with one damage-aware
D3D copy into its final IVSHMEM resource.

Keep only one software copy in flight so newer frames are dropped
instead of queued behind stale work. Retain accumulated damage for the
next frame and skip static re-encodes when no image update is pending.

Use a row-major IVSHMEM texture when the shared heap supports it and
fall back to a direct IVSHMEM buffer copy otherwise. In indirect mode,
copy only damaged rows from readback memory into IVSHMEM.

idd/LGIdd/CD3D12CommandQueue.cpp

@@ -538,7 +538,22 @@ CD3D12CommandSlot * CD3D12CommandQueue::Acquire(UINT slotIndex)
 
 CD3D12CommandSlot * CD3D12CommandQueue::Acquire()
 {
-  return Acquire(0);
+  if (!m_slotCount)
+    return nullptr;
+
+  // The unindexed path is used for immediate software publication. Keep at
+  // most one copy in flight so a newer frame is dropped instead of queued
+  // behind bandwidth-bound work which is already stale.
+  CD3D12CommandSlot& slot = m_slots[0];
+  if (slot.Acquire())
+    return &slot;
+
+  // Complete already-fenced work without waiting for callback dispatch.
+  slot.OnCompletion(false);
+  if (slot.Acquire())
+    return &slot;
+
+  return nullptr;
 }
 
 void CD3D12CommandQueue::WaitForIdle()