Reuse the companion prose.ts rules as the single deterministic detector;
applyable rules feed 'mechanics' suggestion cards via a persist-only
endpoint, awareness rules stay companion bubbles. Mechanics wins span
collisions with LLM cards. Migration 0008 adds the type.
Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd
