Following up on https://github.com/wmde/wikidata-wikibase-architecture/pull/37#issuecomment-762796962 and https://github.com/wmde/wikidata-wikibase-architecture/pull/37#pullrequestreview-571303874, we should document our decision to document Repo as a standalone system and Client as something that is embedded into a MediaWiki application.

As suggested, this should be documented in the "Scope and Context" sections of both subsystems, and could also be documented as a meta decision in the decisions folder.