docs: add council-lite artifacts walkthrough

[dtsong]

Goal

Add a short walkthrough in docs/workflows-playbook.md that explains each core council-lite artifact (intake.md, assembly.md, deliberation/round1-position.md, plan.md).

Why

New users often see generated files but do not know how to read or use them.

Acceptance Criteria

• Add a dedicated subsection for council-lite artifact interpretation
• Explain what each file is for in 1-2 bullets
• Include a suggested review order
• Link back to scripts/validate-council-lite.sh --latest for quick validation