enhancement: add machine-readable output for council-lite list

[dtsong]

Goal

Add a machine-readable output option for ./scripts/council-lite.sh list (for example --json).

Why

This would make it easier to automate follow-up steps (like resuming latest session in scripts) without parsing human-readable text.

Acceptance Criteria

• Add a new flag (for example --json) to list
• Output valid JSON including session id, status, and prompt
• Keep existing default output unchanged
• Update command docs with one usage example