DFT structure relaxation

Variable-cell DFT relaxation with ABACUS (ions + cell). Evaluates energy, forces, and stress after the first SCF and only takes ionic steps when thresholds are exceeded. Returns a relaxed CIF, the relaxation path as an ASE .traj (energy, forces and stress per step), and convergence diagnostics. Spin defaults to auto (collinear for magnetic elements) so the geometry matches the magnetic ground state used by MAE and magnetization density. Pass the relaxed CIF into downstream property routes. Steps taken are kept: a run that stops at its budget, or a worker restart, resumes from the last geometry on the next call with the same input and thresholds.