Platform-wide growth KPIs (platform admin only; aggregates only)

Platform-admin only: allowed when the caller's email (the session user's email, or — for an API key — the owner member's email of the key's organization) is in the server's PLATFORM_ADMIN_EMAILS env var (comma-separated, empty by default). Any other caller gets 404 not_found, not 403, so a self-hosted operator who never sets PLATFORM_ADMIN_EMAILS never sees this endpoint exist. Returns COUNT aggregates across every organization — never emails, names, submission payloads, API keys, or per-organization dumps. Requires the read scope. This is the narrow platform aggregate exception defined by ADR-011. Every value is a current snapshot of retained database rows, so retention and user deletion can reduce totals and window counts; this is not an append-only historical funnel. Sandbox fields are explicitly prefixed retained_ because housekeeping deletes every sandbox after expires_at, including claimed rows. orgs_with_real_delivery_30d is organizations with at least one successful (status=sent) Delivery of a non-test Submission in 30 days.