feat(companion): initial rn port scaffold

aris/app/+not-found.tsx

@@ -0,0 +1,26 @@
+import { Link, Stack } from 'expo-router';
+
+import { Text, View } from 'react-native';
+
+import { Container } from '@/components/Container';
+
+export default function NotFoundScreen() {
+  return (
+    <View className={styles.container}>
+      <Stack.Screen options={{ title: 'Oops!' }} />
+      <Container>
+        <Text className={styles.title}>{"This screen doesn't exist."}</Text>
+        <Link href="/" className={styles.link}>
+          <Text className={styles.linkText}>Go to home screen!</Text>
+        </Link>
+      </Container>
+    </View>
+  );
+}
+
+const styles = {
+  container: `flex flex-1 bg-white`,
+  title: `text-xl font-bold`,
+  link: `mt-4 pt-4`,
+  linkText: `text-base text-[#2e78b7]`,
+};