Adds a Docker Compose dev stack alongside the existing Kind/K8s setup,
giving developers a lighter-weight option and enabling Compose-based CI
integration tests (avoiding KinD-in-DinD cgroup issues).

New files:
- docker-compose.yml: full dev stack (10 services, health checks, seed profile)
- docker-compose.ci.yml: CI override (resource limits, stripped UI ports)
- config/Revolt.compose.toml: Compose-specific config with Docker DNS names

Updated:
- Tiltfile: --compose flag switches between docker_compose() and k8s_yaml()
- justfile: up-compose, compose-up, compose-down, compose-seed targets
- README.md: documents both modes with prerequisites, commands, architecture

Co-Authored-By: Claude Opus 4.6 <[email protected]>