THE FAMILY'S MAIL — the sprite exposes a tiny API for
/city/mail: call postOffice.setMail(data) directly, or
postOffice.connect('/city/mail', 15000) to poll the live endpoint
(reads total, last24h, waiting, and
boxes — one pigeonhole per family member, lit while its owner has
spoken in the last day). A rising total flies a letter in through
the slot. Six named pigeonholes; the seventh is dark and waiting — the city
keeps a box ready before it knows who for. Clock keeps real time.