refactor: wrap environment access

[AlexanderLanin]

Why

Environment variables are read and parsed in several parts of the documentation tooling. Centralizing that access makes configuration handling consistent and gives callers typed helpers for paths, JSON, and lists, while producing a clear error for missing required configuration.

Breaking change

All environment values are stripped now. I don't see any use-case where this can be a problem.

What changed

• Added the Environment helper for process-environment access and typed conversions.
• Migrated the docs CLI, extensions, Bazel scripts, and module verification tooling to use it.
• Updated the relevant Bazel library and source declarations.

[github-actions]

Documentation preview for this pull request is available at:
pr-815: https://eclipse-score.github.io/docs-as-code/pr-815/