Share what's playing in any Android music app

A local Expo module listens to system media sessions (the only way
Android exposes other apps' playback, gated by notification access; we
never read notifications). It filters to known music apps, debounces and
deduplicates changes, sends a heartbeat while playing, and delivers
reports through WorkManager so they survive the app being closed.

- One-screen onboarding that doubles as Google Play's prominent
  disclosure, opening straight to the app's toggle in Android settings
- Only media notifications are pre-ticked on that settings screen
- Device registration is single-flight (several screens react to the
  same permission change) and self-heals if the server revokes a token
- Sign-out revokes the phone's token; resuming sharing re-sends the
  current track immediately
- Pause controls in Settings and on the feed
- Fix invisible tab icons and labels on Android
- Keep Metro out of build output so it doesn't exhaust file watchers

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/mobile/src/app/_layout.tsx

@@ -6,6 +6,7 @@ import { AppState, StyleSheet, View } from 'react-native';
 import { SWRConfig } from 'swr';
 import { Body, Button, Title } from '@/components/ui';
 import { api } from '@/lib/api';
+import { syncDevice } from '@/lib/nowPlayingReader';
 import { SessionProvider, useSession } from '@/lib/session';
 import { colors, space } from '@/lib/theme';
 
@@ -35,6 +36,11 @@ function AppNavigator() {
     if (status !== 'loading') SplashScreen.hideAsync();
   }, [status]);
 
+  // Keep the Android listener pointed at this account (no-op elsewhere).
+  useEffect(() => {
+    if (signedIn) syncDevice().catch(() => {});
+  }, [signedIn]);
+
   if (status === 'loading') return null;
   if (status === 'offline') {
     return (
@@ -69,6 +75,7 @@ function AppNavigator() {
         <Stack.Protected guard={signedIn}>
           <Stack.Screen name="(tabs)" options={{ headerShown: false }} />
           <Stack.Screen name="u/[username]" options={{ title: '' }} />
+          <Stack.Screen name="share-setup" options={{ headerShown: false, presentation: 'modal' }} />
         </Stack.Protected>
         <Stack.Protected guard={!signedIn}>
           <Stack.Screen name="login" options={{ headerShown: false }} />