- JobSystem abstraction over the existing ThreadPool worker pool; the
factory in JobSystem.cpp is the single backend switch point (TBB later).
- Job carries a dependency count and completion callback so a render graph
can be wired on top without rewriting the scheduler.
- parallel_for(first, last, body, chunk) with static partitioning, auto
chunk sizing, and a join handle; task_group provides fork/join with
help-execution so workers can wait without deadlocking.
- Per-frame arena (beginFrame/endFrame) for frame-scoped jobs: no per-frame
new/delete; frame jobs are recycled by the arena.
- Thread module exposes a shared engine JobSystem (getJobSystem).
- VoxelWorld::remeshDirty now uses parallel_for instead of raw std::thread.
- 24 new zeroerr tests in test/thread.cpp; verified with a standalone MSVC
harness (24 cases x 30 runs, no flakes).
