feat: section 4 — Android battery optimization prompt

One-time prompt on first launch (Android only) directing the user to
exclude bincio-rec from battery optimization. Uses the direct
REQUEST_IGNORE_BATTERY_OPTIMIZATIONS system dialog with a fallback to
the general settings page for OEMs that block the direct intent.
Dismissal persisted in AsyncStorage so prompt never repeats.

App.tsx

@@ -4,6 +4,7 @@ import * as Notifications from 'expo-notifications';
 import { GestureHandlerRootView } from 'react-native-gesture-handler';
 import { AppNavigator } from './src/navigation/AppNavigator';
 import { requestNotificationPermissions } from './src/services/gps';
+import { promptBatteryOptimizationIfNeeded } from './src/services/batteryOptimization';
 
 // Show notifications even when the app is in the foreground (iOS suppresses by default)
 Notifications.setNotificationHandler({
@@ -18,6 +19,7 @@ Notifications.setNotificationHandler({
 export default function App() {
   useEffect(() => {
     requestNotificationPermissions();
+    promptBatteryOptimizationIfNeeded();
   }, []);
 
   return (