Forcing every call site to be explicit eliminates a class of bugs where an unintended default silently slips through. Codifies the convention already established by prior commits (cd40483, b41652a, 8eb0f23).
Replace the strict "one commit per file" guidance with grouping by
related changes, while keeping the small-and-focused intent. Add
explicit guidance on when to include a commit body and how to format
it (blank line separator, ~72 col wrap).
Applied to both backend and frontend prompt templates.
