Describe the gateway and shard processes, transparent transfers, the
economy and console peers in the README. Compose creates one Postgres
database per shard and passes `SHARD_DATABASE_URL` and `SIM_SHARDS`;
the Justfile and Dockerfile use per-shard SQLite files.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
