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/app/(tabs)/scan.tsx

@@ -4,6 +4,7 @@ import { Ionicons } from '@expo/vector-icons';
 import { useRouter } from 'expo-router';
 import * as ImagePicker from 'expo-image-picker';
 import { useThemeContext } from '../../components/ThemeProvider';
+import { useTranslation } from '../../src/i18n';
 import { spacing, borderRadius, shadows } from '../../constants/theme';
 
 const TABLET_MIN_WIDTH = 768;
@@ -13,6 +14,7 @@ export default function ScanTabScreen() {
   const { width } = useWindowDimensions();
   const isTablet = width >= TABLET_MIN_WIDTH;
   const { colors } = useThemeContext();
+  const { t } = useTranslation();
   const [manualNumber, setManualNumber] = useState('');
   const [selectedImage, setSelectedImage] = useState<string | null>(null);
 
@@ -20,8 +22,8 @@ export default function ScanTabScreen() {
     const { status } = await ImagePicker.requestCameraPermissionsAsync();
     if (status !== 'granted') {
       Alert.alert(
-        'Permiso requerido',
-        'Necesitamos acceso a la cámara para tomar fotos del dispositivo.'
+        t('scanner.cameraPermission'),
+        t('scanner.cameraPermissionDesc')
       );
       return;
     }
@@ -41,8 +43,8 @@ export default function ScanTabScreen() {
     const { status } = await ImagePicker.requestMediaLibraryPermissionsAsync();
     if (status !== 'granted') {
       Alert.alert(
-        'Permiso requerido',
-        'Necesitamos acceso a la galería para seleccionar fotos.'
+        t('scanner.galleryPermission'),
+        t('scanner.galleryPermissionDesc')
       );
       return;
     }
@@ -61,7 +63,7 @@ export default function ScanTabScreen() {
   const handleManualSubmit = () => {
     const trimmed = manualNumber.trim();
     if (trimmed.length === 0) {
-      Alert.alert('Campo requerido', 'Por favor, introduce el número de la tarjeta.');
+      Alert.alert(t('scanner.fieldRequired'), t('scanner.fieldRequiredDesc'));
       return;
     }
     router.push(`/medicine/${trimmed}`);
@@ -76,9 +78,9 @@ export default function ScanTabScreen() {
         <View style={[styles.iconContainer, isTablet && styles.iconContainerTablet, { backgroundColor: colors.primaryContainer }]}>
           <Ionicons name="scan" size={isTablet ? 80 : 64} color={colors.scanButton} />
         </View>
-        <Text style={[styles.title, isTablet && styles.titleTablet, { color: colors.text }]}>Escanear TSI</Text>
+        <Text style={[styles.title, isTablet && styles.titleTablet, { color: colors.text }]}>{t('scanner.title')}</Text>
         <Text style={[styles.description, isTablet && styles.descriptionTablet, { color: colors.textSecondary }]}>
-          Escanea el código de barras de tu tarjeta sanitaria para encontrar tus medicamentos
+          {t('scanner.description')}
         </Text>
         <TouchableOpacity
           style={[styles.primaryButton, shadows.scanButton, isTablet && styles.primaryButtonTablet]}
@@ -87,14 +89,14 @@ export default function ScanTabScreen() {
         >
           <Ionicons name="scan" size={isTablet ? 28 : 24} color="#ffffff" />
           <Text style={[styles.primaryButtonText, isTablet && styles.primaryButtonTextTablet]}>
-            Iniciar escaneo
+            {t('scanner.startScan')}
           </Text>
         </TouchableOpacity>
 
         {/* Separator */}
         <View style={styles.separator}>
           <View style={[styles.separatorLine, { backgroundColor: colors.border }]} />
-          <Text style={[styles.separatorText, { color: colors.textSecondary }]}>o</Text>
+          <Text style={[styles.separatorText, { color: colors.textSecondary }]}>{t('scanner.or')}</Text>
           <View style={[styles.separatorLine, { backgroundColor: colors.border }]} />
         </View>
 
@@ -103,10 +105,10 @@ export default function ScanTabScreen() {
           <Ionicons name="camera" size={24} color={colors.primary} />
           <View style={styles.optionTextContainer}>
             <Text style={[styles.optionTitle, isTablet && styles.optionTitleTablet, { color: colors.text }]}>
-              Subir foto del dispositivo
+              {t('scanner.uploadPhoto')}
             </Text>
             <Text style={[styles.optionDescription, isTablet && styles.optionDescriptionTablet, { color: colors.textSecondary }]}>
-              Toma o selecciona una foto del dispositivo sanitario
+              {t('scanner.uploadDescription')}
             </Text>
           </View>
         </View>
@@ -117,7 +119,7 @@ export default function ScanTabScreen() {
             onPress={handleTakePhoto}
           >
             <Ionicons name="camera-outline" size={20} color={colors.primary} />
-            <Text style={[styles.photoButtonText, { color: colors.primary }]}>Tomar foto</Text>
+            <Text style={[styles.photoButtonText, { color: colors.primary }]}>{t('scanner.takePhoto')}</Text>
           </TouchableOpacity>
           <TouchableOpacity
             style={[styles.photoButton, isTablet && styles.photoButtonTablet, { backgroundColor: colors.primaryContainer, borderColor: colors.primary }]}
@@ -125,13 +127,13 @@ export default function ScanTabScreen() {
             onPress={handleSelectFromGallery}
           >
             <Ionicons name="images-outline" size={20} color={colors.primary} />
-            <Text style={[styles.photoButtonText, { color: colors.primary }]}>Galería</Text>
+            <Text style={[styles.photoButtonText, { color: colors.primary }]}>{t('scanner.gallery')}</Text>
           </TouchableOpacity>
         </View>
         {selectedImage && (
           <View style={styles.imagePreviewContainer}>
             <Ionicons name="checkmark-circle" size={20} color={colors.success} />
-            <Text style={[styles.imagePreviewText, { color: colors.success }]}>Foto seleccionada correctamente</Text>
+            <Text style={[styles.imagePreviewText, { color: colors.success }]}>{t('scanner.photoSelected')}</Text>
           </View>
         )}
 
@@ -140,17 +142,17 @@ export default function ScanTabScreen() {
           <Ionicons name="keypad" size={24} color={colors.primary} />
           <View style={styles.optionTextContainer}>
             <Text style={[styles.optionTitle, isTablet && styles.optionTitleTablet, { color: colors.text }]}>
-              Introducir número manualmente
+              {t('scanner.manualEntry')}
             </Text>
             <Text style={[styles.optionDescription, isTablet && styles.optionDescriptionTablet, { color: colors.textSecondary }]}>
-              Escribe el número de tu tarjeta sanitaria
+              {t('scanner.manualDescription')}
             </Text>
           </View>
         </View>
         <View style={styles.manualInputRow}>
           <TextInput
             style={[styles.manualInput, isTablet && styles.manualInputTablet, { backgroundColor: colors.card, borderColor: colors.border, color: colors.text }]}
-            placeholder="Introduce el número de tarjeta"
+            placeholder={t('scanner.manualPlaceholder')}
             placeholderTextColor={colors.textSecondary}
             value={manualNumber}
             onChangeText={setManualNumber}