docs: document story engine and PR2 playable loop

docs/architecture.md

@@ -12,6 +12,8 @@ Idlegame is split into four layers.
   queue advancement (actions do not auto-repeat when the queue is empty).
 - `save.ts`: versioned save schema, serialized export/import strings, and
   offline elapsed calculation.
+- `story.ts`: story graph traversal, triggers (boot, actionComplete,
+  minResources), choices, outcomes.
 - `num.ts`: branded numeric boundary and human-readable formatting.
 
 The engine must stay pure. It does not import React, Zustand, browser APIs,
@@ -33,6 +35,9 @@ story nodes, automation unlocks, and prestige definitions.
 - requestAnimationFrame loop and lifecycle hooks
 - mapping engine state to view models
 - Zustand store updates for React
+- `storyOrchestration.ts`: evaluates triggers after boot/publish/action
+  completion; maps prefs to panel auto-open.
+- Player prefs (`prefs.ts`) in localStorage — not in save v1.
 
 ## UI