fix(mobile): align background, API config, and search bar with PWA

- Add background image matching PWA (bg.png with opacity + overlay)
- Fix production API URL to farmacias.hacecalor.net
- Replace raw fetch calls in alerts.tsx with configured api service
- Constrain SearchBar max-width to 420px to prevent horizontal clipping

apps/frontend-mobile/components/SearchBar.tsx

@@ -69,6 +69,9 @@ const styles = StyleSheet.create({
     paddingVertical: spacing.sm + 2,
     marginHorizontal: spacing.lg,
     marginVertical: spacing.sm,
+    maxWidth: 420,
+    alignSelf: 'center',
+    width: '100%',
     shadowColor: '#000',
     shadowOffset: { width: 0, height: 2 },
     shadowOpacity: 0.06,