Deployment infrastructure: Docker, Helm, and release pipeline

## Description

No containerization or deployment infrastructure exists beyond CI workflows. The project needs:

1. **Dockerfile** for the worldcompute binary
2. **Docker Compose** for local multi-node testing
3. **Kubernetes manifests** or Helm chart for coordinator deployment
4. **Release pipeline**: reproducible builds, code signing, binary distribution
5. **Staged release gates** per whitepaper (Phase 0→1→2→3→4)

## Requirements

- Multi-stage Dockerfile (build + runtime) with minimal attack surface
- Docker Compose for 3-node local cluster testing
- Helm chart for coordinator nodes on K8s
- Reproducible build configuration (deterministic compilation)
- Code signing for release binaries (per FR-005)
- Release channel enforcement: dev → staging → production (no skip)
- Binary distribution for Linux (x86_64, aarch64), macOS (Apple Silicon), Windows

## Success Criteria

- [ ] `docker build` produces minimal container image
- [ ] `docker compose up` creates functional 3-node cluster
- [ ] Helm chart deploys coordinator set on K8s
- [ ] Release binaries are reproducibly built and code-signed
- [ ] Release channels enforce sequential promotion
- [ ] Binary downloads available for all target platforms

## Testing (Principle V)

- Build and run container → verify agent functionality
- Docker Compose 3-node cluster → verify peer discovery and job execution
- Helm deploy on real K8s → verify coordinator election
- Verify binary reproducibility (two builds produce identical output)