Default study layout to split view

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.jsx

@@ -913,7 +913,7 @@ const App = () => {
     }
   }, []);
   const [studyLayout, setStudyLayout] = useState(
-    () => localStorage.getItem('studyLayout') || 'stacked',
+    () => localStorage.getItem('studyLayout') || 'split',
   ); // 'stacked' | 'split' | 'annotate'
   const [drawTool, setDrawTool] = useState('pen');
   const [drawColor, setDrawColor] = useState('#0f172a');