document-decision

Create Architecture Decision Records (ADRs) in docs/arc42/decisions/. Use when user says 'document this decision', 'create an ADR', 'record architecture decision', 'why did we choose X', 'document the rationale', or when adding major dependencies, new frameworks, or changing fundamental patterns. Do NOT use for user-facing feature docs (use /document-feature) or syncing existing docs (use /update-doc).