`plan` — Feature Plan Creator

Turns a feature description into a task-by-task implementation plan and writes it to docs/superpowers/plans/<YYYY-MM-DD>-<feature-slug>/PLAN.md.

Position in the gflow-cli workflow:

/gflow:predict <proposal>   →  GO / CAUTION / STOP verdict
/gflow:scenario <feature>   →  edge cases + BDD skeleton
/gflow:plan <feature>       →  writes the task checklist  ← this skill
/gflow:status               →  surfaces next task during execution
/gflow:check                →  before each commit