Add mock API and reorg code for clarity

src/view/screens/Notifications.tsx

@@ -0,0 +1,14 @@
+import React from 'react'
+import {Shell} from '../shell'
+import {Text, View} from 'react-native'
+import type {RootTabsScreenProps} from '../routes/types'
+
+export const Notifications = (_props: RootTabsScreenProps<'Notifications'>) => {
+  return (
+    <Shell>
+      <View style={{justifyContent: 'center', alignItems: 'center'}}>
+        <Text style={{fontSize: 20, fontWeight: 'bold'}}>Notifications</Text>
+      </View>
+    </Shell>
+  )
+}