fableplan

Use when the user wants a task planned by a Fable 5.1 planning subagent before building it. Spins up a Plan subagent running on Fable 5.1 to produce an implementation plan, relays the plan back to the main agent, and — if a GitHub issue is referenced — posts the plan as a comment on that issue and asks the user whether to continue building now before proceeding. Trigger on "/fableplan", "fableplan this", or "plan…