Give neural_attractor and neural_reversible a machine metadata field and eval_all skip entries, so python src/eval_all.py variants/ skips them cleanly instead of erroring (it scores fitness variants and skips standalone machines by that field). README sync: list both new machines in the variant table, intro, and repository layout; correct the standalone-machine count (5->7), the eval_all skip count (four->seven), and the universal-constructor family round-trip (23->26 files, 551->971 MB, both new files codec-verified byte-identical).

neural_reversible: ship the reversible arithmetic core as variants/neural_reversible.safetensors (8-bit in-place adder as a reversible gate sequence plus the Heaviside weights realizing each gate); builder round-trips it and confirms the loaded circuit is a bijection computing b<-a+b