Multi-tenancy wiki: per-sender-address routing, freemail list, routing diagnostics (#563-567)
Multi-tenancy wiki: mark Phase 1 tickets + Phase 2 email routing as built Progress tracker: count badges done; Phase 2 (pinned/shared mailboxes, domain routing, triage queue, freemail handling) now complete bar outbound reply identity. Email-routing + landing pages updated from 'planned' to 'built on the multi-tenancy branch'. Parked ideas (routing visualiser, customisable freemail list) noted.
Add Multi-tenancy section (9 pages: design, routing, settings, self-service, worked examples, pitfalls, scope)