feat(spec): give state.lastAction an applied field

Three states, not two: no action is a null lastAction, applied: true is an
action the runner confirmed, applied: null is one it dispatched and never
learned the fate of.

pkg/spec/src/index.ts

@@ -12,6 +12,7 @@ export type {
   InputTextAction,
   Key,
   KnownAttrSelectors,
+  LastAction,
   LogEntry,
   Point,
   PressKeyAction,