refactor(docker): image size reduction, standardisation, security hardening (#25)

* chore: add Docker build tooling and linting config

* ci: add DHI registry support

* chore: add Java dependency checksums for supply chain security

* chore: update Go and Rust dependencies

* refactor(docker): consolidate Python requirements

* feat(docker): migrate API image to DHI base

* feat(docker): migrate sidecar to DHI base

* feat(docker): migrate language images to DHI base

* refactor: standardise on UID 65532