Create a plan document using the superseded v1 workflow — it writes no `Format: v2` marker and no execution.md tracker. Use when the user invokes /plan-init-v1, or is continuing an existing v1 plan; new work belongs to /plan-init. Interviews the user to fill gaps, explores the codebase for context, then produces a master plan with goal, success criteria (checkable tests/conditions), technical constraints, non-goals, and affected areas. Does NOT break the plan into phases — use /plan-phase-v1 for that.
