Progressive 50/50 Sigma Control

Side-channel control for progressive transcode workflows: when the low-res to high-res branch is active and this node is connected to Sampling Plan (Wan 2.2), Low-only acceleration uses the accelerated step budget split 50/50 for the sigma curve while preserving Low-only model and CFG routing. Because it is not in the required plan chain, it can be muted with its group.