Follow-up-cadence tracker (low-code -> full-code rung)

Where a business app starts wanting real logic — the rung tilts toward full-code. It reads your leads/contacts sheet, computes days-since-last-touch, and flags who's due. This chains the sheet-pipeline pattern from B11 and previews B12's cron without requiring a deploy: ship the logic first, scheduling is optional stretch. The value is that no lead goes cold because you forgot which day they were on.