Docs Eval Planning

Plan a documentation eval for supabase/evals, where a docs guide is the subject under test. Use when asked to write, add, or design an eval for a Supabase docs guide, when a ticket asks for a deterministic eval on a page, or when deciding what a guide-under-test eval should check. Produces a plan, not files. Not for debugging a scorer, running an eval, or writing example solutions.