OcclusionPassContext

Forward-draw hook fired AFTER the deferred composite. The consumer (points / splats) draws straight into the finished frame, whose depth attachment is BORROWED from the capture G-buffer, so its fragments depth-test against the real BIM depth (occluded behind walls) — Phase-1 occlusion, no shader patch. Mirrors the old DeferredPipeline's OcclusionPass contract (direct mode).