Scrooge & Marley — The Dead Letter Office — automated dunning correspondence extension

Technical specification for The Dead Letter Office — the Scrooge & Marley automated dunning correspondence extension. Covers the business case, template engine with handlebars variables, escalation registers, database schema (3 new tables), Vercel cron trigger design, despatch log constraints, and effort estimate. After reading, a developer can assess fit and begin implementation within the Marley Next.js template.