Add mock API and reorg code for clarity

src/screens/Home.tsx

@@ -1,21 +0,0 @@
-import React from 'react'
-import {Text, Button, View} from 'react-native'
-import {Shell} from '../platform/shell'
-import type {RootTabsScreenProps} from '../routes/types'
-import {useStores} from '../state'
-
-export function Home({navigation}: RootTabsScreenProps<'Home'>) {
-  const store = useStores()
-  return (
-    <Shell>
-      <View style={{alignItems: 'center'}}>
-        <Text style={{fontSize: 20, fontWeight: 'bold'}}>Home</Text>
-        <Button
-          title="Go to Jane's profile"
-          onPress={() => navigation.navigate('Profile', {name: 'Jane'})}
-        />
-        <Button title="Logout" onPress={() => store.session.logout()} />
-      </View>
-    </Shell>
-  )
-}