Planning workflows loaded document_output_language from config but never
enforced it in step files. Only communication_language was enforced,
causing generated artifacts (product briefs, PRDs, UX specs, project
docs) to be written in the conversation language instead of the
configured document output language.
Add explicit document_output_language enforcement in all content-
generating step files across create-product-brief, create-prd,
create-ux-design, generate-project-context, and document-project
workflows.
Closes#1966
Alex Verkhovsky