feature: compiled-binary e2e smoke

e2e drives Deployah in-process via nabattest.Run. That misses argv, exit codes, signals, and a broken nix run / release binary.

Add a thin compiled-binary smoke: build deployah once, run version / --help and a couple of known exit codes. One short cluster command is optional if it stays cheap. This does not replace the Kind deploy smoke.

In-process e2e stays the main suite.