Task book for the render-pipeline rearchitecture: one decode thread
and one render thread feeding queue-linked stages with the main
process presenting (the GPU's single queue makes the multi-process
backend dead weight), one dedicated OpenFX host process with
bounded respawn, GPU-resident frames end-to-end except at the CPU
OFX/export/cache boundaries, a per-backend interop table, and the
resolve rewrite to a single-loop match over a completed Job enum
(CacheJob included) following upstream Olive's
NodeTraverser::ResolveJobs. Milestones M0-M5 with the thread backend
kept behind an OAK_PIPELINE fallback switch.
