docs: document story engine and PR2 playable loop

src/state/viewModel.ts

@@ -2,8 +2,8 @@ import type { GameContent } from '../content/index';
 import {
   canAffordAction,
   canUnlockAction,
-  isActionAvailable,
   type GameState,
+  isActionAvailable,
 } from '../engine/game';
 import { getAvailableChoices, getCurrentNode } from '../engine/story';