Tab bar icon sizes and labels follow platform guidelines

Sub-20pt tab bar icons are below the WCAG 2.2 SC 2.5.5 target-size threshold (44x44pt minimum) and the Apple HIG 49pt tab bar height — users with average thumb size mis-tap, and users with motor impairments cannot hit the target at all. Missing labels force users to memorize pictographs, which harms first-session discoverability and is specifically flagged by Google Play's user experience quality signals.

Set explicit icon sizes of at least 24pt, show labels on every tab, and set platform-appropriate tab bar heights in @react-navigation/bottom-tabs:

<Tab.Navigator screenOptions={{
  tabBarIconStyle: { width: 24, height: 24 },
  tabBarStyle: { height: Platform.OS === 'ios' ? 83 : 56 },
  tabBarShowLabel: true,
}}>
  <Tab.Screen name="Home" component={HomeScreen} options={{ tabBarLabel: 'Home' }} />
</Tab.Navigator>