Add 'nsbx dev <name>' / 'nsbx dev-down <name>' plus a Makefile so a newcomer
goes from clone to coding on an isolated cloned engram in one command. The
worktree is created on a real named branch at a persistent path (never /tmp,
guarded), and the whole worktree is pinned to the clone via an emitted .nsbx-env
so live :8742 / ~/.neuron/engram is unreachable by accident. Optimizes the El
edit->build->run loop so provisional work is built in El against a throwaway
clone instead of prototyped in Python and re-ported. Additive over the proven
primitives; no live cutover.
bigmerge