backlog-planner

Turn a feature idea, conversation context, or rough notes into researched, detailed, dependency-ordered checkbox tasks appended to the project's roadmap/backlog file — exactly the format goal-runner consumes, so a fresh unattended session can execute them. Grounds every task in the actual codebase before writing it (grep/read or Explore scouts; think-like-fable rigor if installed), puts what + done-when on the checkbox line with verified files, acceptance criteria, and a verification command in plain sub-bullets, and labels assumptions. Appends to the existing ROADMAP.md/BACKLOG.md/TODO.md; wh