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/app/(tabs)/index.tsx

@@ -100,7 +100,10 @@ const styles = StyleSheet.create({
   searchContainer: {
     flexDirection: 'row',
     alignItems: 'center',
-    paddingRight: spacing.lg,
+    paddingHorizontal: spacing.lg,
+    maxWidth: 480,
+    alignSelf: 'center',
+    width: '100%',
   },
   searchContainerTablet: {
     maxWidth: 700,