VASP optcell/native cell and atomic degrees-of-freedom tutorial

Replot three PNG / two CSV from actual reference numbers:
  bash run.sh

First full fifteen-case calculation in a fresh project:
  bash prepare.sh
  bash calculate.sh
  bash status.sh
When all jobs finish:
  bash verify.sh

prepare uses VASPKIT1.5.1 task103 for licensed SiPBE POTCAR; not included.
New native outputs and figures are in work/, reference replot in outer directory.
Keep SUBMISSIONS.json; do not submit completed tasks a second time.
VASP6.6.1 native/optcell, NVHPC25.3/MKL2023.2, ENCUT550/4x4x4Gamma/EDIFF1e-6.
Positions-relaxing cases use force0.02eV/A. ISIF5/6 freezes fractional positions;
these cell-only cases use EDIFFG=+1e-6eV energy change and check allowedstress.
NativeFFF example in invalid-example is intentionally rejected beforeSCF and notsubmitted bycalculate.sh.
Original displaced-Si ISIF5/6 negative force-stop attempts retained separately
in private research record; they were not force-converged and are not positive cases.
ISIF0 has no stress and ISIF1 has only reliable trace, not full tensor.
Fifteen valid cases cover ISIF0/1/5/6/8 and default/allone/allzero/xz masks.
Combined with the preceding tutorial ISIF2/3/4/7 cases this explains each ISIF0..8
branch. It is not an exhaustive enumeration of all arbitrary nine-integer masks,
all materials or pulay/kmesh convergence.
All-zero masks freeze the cell but still relax atoms. No IOPTCELL in optcell
build behaves like all-one for this test. ISIF5/6 frozenfractional positions
can retain nonzero forces; Cartesian positions may change due to cell deformation.
