Artifact: Relocated Design Doc — Notification Worker Architecture

A drifted wiki design doc, moved close to the code and dated -- exercises co-17.

Action: delete the wiki page. Move its accurate remaining content (deployment topology, which has not changed) into services/notification-worker/docs/architecture.md, dated at the top with today's date, and rewrite the event-consumption section to describe the actual current Kafka-based design (ADR-0005). Add a one-line pointer in notification_worker/README.md: "Full architecture: see docs/architecture.md."

Frontmatter added: Date: 2026-03-19 (last verified against the running code).