Closes round 4 of doc-prep. ARCHITECTURE.md is the day-1 read for engineers joining Cyclone: process & network topology, tech stack (backend + frontend + external), backend package layout with one-line module responsibility map, frontend architecture (route map, state management, live tail), data model (migrations 0001-0012, ERD, 7-state claim lifecycle, audit chain), data flow (manual upload, SFTP polling, auto-match, outbound 837P, ack ingestion), API surface, cross-cutting concerns (logging, audit, PHI/PII, error model), operational concerns (startup order, schedulers, health probe, shutdown), deployment, out-of-scope, and references. 759 lines, 13 top-level sections. Cross-linked from REQUIREMENTS.md sister-docs block and from README.md Roadmap section.
38 functional requirements + 18 non-functional requirements across 13 sections. Includes traceability matrix mapping FRs to NFRs and to existing docs/superpowers/specs/* artifacts. Closes round 1 of doc-prep preparation for Cyclone implementation.
Tyler