Heal GitHub installs stranded with an empty repository set (internal sweep).

The platform-wide backstop for the miss github_refresh fixes one tenant at a time: an install whose repositories were still empty on every read inside the callback's budget is committed empty, and nothing ever re-reads it. This sweep re-reads every such install under the launcher identity -- so a stuck install heals without the user pressing Retry, and every future one heals until the installation.created webhook backstop lands. Pass tenantId to force-refresh a single tenant's installs (a one-off) instead of sweeping the empty-set backlog.

Scheduled alongside the reindex-catchup sweep; a no-op when nothing is stuck, so it is safe to run unconditionally. SETTINGS_MANAGE is not required (and no user context exists here) because the launcher identity, not a tenant admin, drives it.