feat(i18n-mobile): add bilingual support (Català / Castellano) for React Native app

Add lightweight i18n system matching the web app architecture.
Language persisted in AsyncStorage('ff-lang').

New files:
- src/i18n/locales/ca.js (~190 translation keys)
- src/i18n/locales/es.js (~190 translation keys)
- src/i18n/LanguageContext.jsx (Provider + AsyncStorage)
- src/i18n/useTranslation.js (hook)
- src/i18n/index.js (barrel export)

Modified 16 files:
- app/_layout.tsx: wrap with LanguageProvider, translate stack titles
- app/(tabs)/_layout.tsx: translate tab bar labels
- app/(tabs)/index.tsx: translate home screen
- app/(tabs)/search.tsx: translate search screen
- app/(tabs)/alerts.tsx: translate alerts screen
- app/(tabs)/profile.tsx: translate profile + add language selector (CA/ES)
- app/(tabs)/scan.tsx: translate scanner screen
- app/auth/login.tsx: translate login/register
- app/medicine/[id].tsx: translate medicine detail
- app/pharmacy/[id].tsx: translate pharmacy detail
- app/product/[source]/[id].tsx: translate product detail
- 5 components: MedicineCard, StockBadge, SearchBar, LoadingSpinner, BarcodeScanner

Language selector in Profile screen (globe icon + CA/ES toggle).
No routes changed. No API calls affected.

apps/frontend-mobile/components/BarcodeScanner.tsx

@@ -4,6 +4,7 @@ import { CameraView, useCameraPermissions } from 'expo-camera';
 import { Ionicons } from '@expo/vector-icons';
 import { useThemeContext } from './ThemeProvider';
 import { spacing, borderRadius } from '../constants/theme';
+import { useTranslation } from '../src/i18n';
 
 interface BarcodeScannerProps {
   onBarcodeScanned: (barcode: string) => void;
@@ -14,6 +15,7 @@ export function BarcodeScanner({ onBarcodeScanned, onClose }: BarcodeScannerProp
   const [permission, requestPermission] = useCameraPermissions();
   const [scanned, setScanned] = useState(false);
   const { colors } = useThemeContext();
+  const { t } = useTranslation();
 
   if (!permission) {
     return <View style={styles.container} />;
@@ -23,15 +25,15 @@ export function BarcodeScanner({ onBarcodeScanned, onClose }: BarcodeScannerProp
     return (
       <View style={[styles.permissionContainer, { backgroundColor: colors.background }]}>
         <Ionicons name="camera" size={64} color={colors.textSecondary} />
-        <Text style={[styles.permissionTitle, { color: colors.text }]}>Permiso de cámara requerido</Text>
+        <Text style={[styles.permissionTitle, { color: colors.text }]}>{t('barcodeScanner.permissionRequired')}</Text>
         <Text style={[styles.permissionText, { color: colors.textSecondary }]}>
-          Necesitamos acceso a la cámara para escanear códigos de barras
+          {t('barcodeScanner.permissionDesc')}
         </Text>
         <TouchableOpacity style={[styles.permissionButton, { backgroundColor: colors.primary }]} onPress={requestPermission}>
-          <Text style={styles.permissionButtonText}>Conceder permiso</Text>
+          <Text style={styles.permissionButtonText}>{t('barcodeScanner.grantPermission')}</Text>
         </TouchableOpacity>
         <TouchableOpacity style={styles.cancelButton} onPress={onClose}>
-          <Text style={[styles.cancelButtonText, { color: colors.textSecondary }]}>Cancelar</Text>
+          <Text style={[styles.cancelButtonText, { color: colors.textSecondary }]}>{t('barcodeScanner.cancel')}</Text>
         </TouchableOpacity>
       </View>
     );
@@ -63,7 +65,7 @@ export function BarcodeScanner({ onBarcodeScanned, onClose }: BarcodeScannerProp
         </View>
         
         <Text style={styles.instruction}>
-          Apunta la cámara al código de barras del medicamento
+          {t('barcodeScanner.scanningHint')}
         </Text>
         
         <TouchableOpacity style={styles.closeButton} onPress={onClose}>
@@ -77,7 +79,7 @@ export function BarcodeScanner({ onBarcodeScanned, onClose }: BarcodeScannerProp
             style={[styles.scanAgainButton, { backgroundColor: colors.primary }]}
             onPress={() => setScanned(false)}
           >
-            <Text style={styles.scanAgainText}>Escanear de nuevo</Text>
+            <Text style={styles.scanAgainText}>{t('barcodeScanner.scanAgain')}</Text>
           </TouchableOpacity>
         </View>
       )}