Top-level supervisor for the Fact runtime.

Fact.Supervisor is the root of the supervision tree and is responsible for bootstrapping and supervising database instances. It coordinates database startup through Fact.Bootstrapper processes and supervises the resulting database processes for the lifetime of the system.

At application startup, any database paths provided via the :databases option are bootstrapped automatically. Additional databases may be started at runtime with start_database/1, which bootstraps a database from the given path and returns its database identifier on success.

This supervisor also owns the global Fact.Registry, which is used for process and Fact.Context lookup across the system.