Substations editor

Substation single-line + earthing grid editor. Bay layouts (single-busbar, double-busbar, 1.5-CB), VT/CT positioning, switchgear coordination, ground grid sizing per IEEE 80.

Phase 2 — uses the same canvas + parameter engine as Electrical Networks. Currently the Networks editor handles general LV/MV cases. The substation-specific bay templates, IEEE 80 grid, and VT/CT placement land in the next iteration.