docs: document story engine and PR2 playable loop

src/ui/App.tsx

@@ -30,6 +30,7 @@ export function App() {
             <div className="flex items-center gap-2">
               <button
                 type="button"
+                aria-label={storyHasUnread ? 'Story, unread' : 'Story'}
                 onClick={() => gameRuntime.openStoryPanel()}
                 className="relative rounded-lg border border-slate-700 bg-slate-800/70 px-3 py-1.5 text-sm transition-colors hover:border-amber-500/60"
               >
@@ -37,7 +38,7 @@ export function App() {
                 {storyHasUnread ? (
                   <span
                     className="absolute -top-1 -right-1 h-2 w-2 rounded-full bg-amber-500"
-                    aria-label="Unread story"
+                    aria-hidden
                   />
                 ) : null}
               </button>

src/ui/SettingsDrawer.tsx

@@ -1,5 +1,5 @@
-import { useGameStore } from '../state/store';
 import type { ActionDetailMode, StoryOpenMode } from '../state/prefs';
+import { useGameStore } from '../state/store';
 
 /** Preference panel toggled from the header gear; changes persist immediately. */
 export function SettingsDrawer() {

src/ui/StoryPanel.tsx

@@ -24,8 +24,8 @@ export function StoryPanel() {
             Story log
           </h3>
           <ul className="flex flex-col gap-2 text-slate-300 text-sm">
-            {storyLog.map((entry, i) => (
-              <li key={`${entry.nodeId}-${i}`}>
+            {storyLog.map((entry) => (
+              <li key={`${entry.nodeId}:${entry.choiceLabel ?? ''}:${entry.prose}`}>
                 {entry.choiceLabel ? (
                   <span className="text-amber-400/80">[{entry.choiceLabel}] </span>
                 ) : null}