Wires the prefork primitive into a CLI command. 'decnet fleet heavy' imports
the shared base floor once in the master, then forks profiler + ttp as
CoW-sharing child processes (own process/GIL, full isolation, shared ~71MB
floor). DB-only tier => systemd unit carries no extra privilege (prefork's
privilege-union cost is nil for this fleet). Unit Conflicts= the profiler/ttp
units it replaces. Heavy per-worker state (ATT&CK/ML) still loads per-child;
warming it in the master to share is deferred until a live RSS measurement
shows the big object graph CoW-shares rather than refcount-dirties.
