* Implement GitHub Actions workflow for Docker image build and release
* Validate release tags and manage Docker login credentials
* Build and push Docker images with versioning and metadata
* Add docker-build target to Makefile for local image building
Replace the ad-hoc tables/procedures install layout with versioned,
ordered SQL migrations tracked in broker_schema_migrations. Add
optional least-privilege role provisioning (--with-roles), multi-tenant
row-level security, lease-based job claiming with stale-lease recovery,
and job dependencies -- both by job id and by fan-in job group. Add
Docker/Compose support for running the broker and its test suite.