chore: upgrade dune toolchain to 3.23.0

[sabine]

Summary

• build dune 3.23.0 from the official release tarball instead of the archived dune-bin-install path
• bump the published dev-base and backend-builder-base image versions to 3.0.0 and update consumer examples
• keep the deprecated ci-node-pnpm-dune image in sync for anyone still using it manually

Validation

• docker build -t makerprism-dev-base-3-test /home/sabine/containers/images/dev-base
• docker build -t makerprism-backend-builder-base-3-test /home/sabine/containers/images/backend-builder-base
• docker build -t makerprism-ci-node-pnpm-dune-3-test /home/sabine/containers/images/ci-node-pnpm-dune
• docker run --rm makerprism-dev-base-3-test sh -lc 'dune --version && ocaml -version && pnpm --version'