The map under churn: closing a blocker as dropped frees what waited on it, and nothing says an issue was split, parked or dropped #416

From the audit in #385 (the map stays readable under churn).

What is there. src/core/dependencies.ts counts only open issues; a closed blocker stops blocking whatever the reason. Words ready/waiting/parked are derived on the map.

What is missing. Closing a blocker because it was dropped or replaced makes its dependents ready and the crew may start them on a plan that no longer holds. Splitting an issue leaves the old edges on the parent. Nothing records why an issue closed (done, dropped, split into N).

Done when. Closing takes a reason: done frees dependents; dropped or split holds them as parked with the reason until a person relinks or confirms; split moves the parent's blocked-by edges to its children. Tests for each, plus the map showing the reason.

Parked by the crew: the preview's deploy failed and the decider saw no point in another try (pull #441 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.