Closes out the producer-side of the diplomail surface. Paid-tier
players can fan out one personal message to the rest of the active
roster (gated on entitlement_snapshots.is_paid). Site admins gain a
multi-game broadcast (POST /admin/mail/broadcast with `selected` /
`all_running` scopes) and the bulk-purge endpoint that wipes
diplomail rows tied to games finished more than N years ago. An
admin listing (GET /admin/mail/messages) rounds out the
observability surface.
EntitlementReader and GameLookup are new narrow deps wired from
`*user.Service` and `*lobby.Service` in cmd/backend/main; the lobby
service grows a one-off `ListFinishedGamesBefore` helper for the
cleanup path (the cache evicts terminal-state games so the cache
walk is not enough). Stage D will swap LangUndetermined for an
actual body-language detector and add the translation cache.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Ilia Denisov
362f92e520