Converts a PRD or requirements document into a structured, phased implementation plan with individual phase files and granular per-task files written to .context/plans/. Also restructures existing monolithic planning documents into digestible, hierarchical directory structures. Creates a root plan index summarising all phases, a numbered phase file per phase, and a numbered task file per task inside each phase directory. Use when the user asks to create an implementation plan, break down a PRD, convert requirements to tasks, structure project phases, generate a roadmap, plan a project in sprints, organise task breakdown, split a monolithic planning doc, or decompose a spec into phases and tasks.