fix: wrap root layout in flex:1 View so Stack fills full screen alongside hidden WebView

mobile/app/_layout.tsx

@@ -1,12 +1,13 @@
 import { Stack } from 'expo-router';
 import { SQLiteProvider } from 'expo-sqlite';
 import { StatusBar } from 'expo-status-bar';
+import { StyleSheet, View } from 'react-native';
 import { migrateDb } from '@/db';
 import { PyodideWebView } from '@/extraction/PyodideWebView';
 
 export default function RootLayout() {
   return (
-    <>
+    <View style={styles.root}>
       {/* Hidden WebView: starts loading Pyodide immediately so the runtime
           is warm by the time the user opens the Import tab. */}
       <PyodideWebView />
@@ -14,6 +15,10 @@ export default function RootLayout() {
         <StatusBar style="light" />
         <Stack screenOptions={{ headerShown: false }} />
       </SQLiteProvider>
-    </>
+    </View>
   );
 }
+
+const styles = StyleSheet.create({
+  root: { flex: 1 },
+});