rgpot kernel inventory

eOn-6yzk is the migration epic. This is the current split, not a claim that the epic is done.

Already in rgpot (used via headers / FortranPots)

LJ, LJ cluster, Morse, ZBL, D3, D4, Expr, MOPAC, and the Fortran kernels (SW, EDIP, Tersoff, Lenosky, EAM-Al, FeHe, CuH2, TIP4P-H) when with_fortran_pots is on.

Highway SIMD for Morse/LJ belongs in rgpot, not client/potentials.

Still in-tree (engines / adapters)

Tree	Why it stays
ASE / ASE_NWCHEM / ASE_ORCA	Python calculator adapters
AMS / AMS_IO / VASP / LAMMPS / MPIPot / ExtPot / SocketNWChem	subprocess / file engines
Metatomic / XTBPot	optional heavy engines (also have rgpot engine .so loaders)
EMT / EAM / Water / Water_Pt / GPR / CatLearn	not yet in rgpot

Adding a new empirical kernel should go to rgpot first.