Org migration: update Docker images and registry paths

[zeevdr]

Description

Update all Docker image references from `ghcr.io/zeevdr/` to `ghcr.io/opendecree/`.

Files to update

• `.github/workflows/ci.yml` — TOOLS_IMAGE env var
• `.github/workflows/release.yml` — REGISTRY, image tags
• `docker-compose.yml` / `docker-compose*.yml` — image references
• `build/Dockerfile`, `build/Dockerfile.tools`, `build/Dockerfile.decree` — if they reference the registry
• `deploy/helm/` — chart values, image repository defaults
• `README.md` — Docker pull instructions

Depends on

• Org migration: create fresh repos with clean history #170 (fresh repos created)

Acceptance criteria

• All ghcr.io/zeevdr references → ghcr.io/opendecree
• `docker compose build` succeeds
• Helm chart defaults updated

[zeevdr]

Completed — migrated to opendecree org.