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)/alerts.tsx

@@ -6,6 +6,7 @@ import { useThemeContext } from '../../components/ThemeProvider';
 import { useAuth } from '../../hooks/useAuth';
 import { spacing, borderRadius, shadows } from '../../constants/theme';
 import { LoadingSpinner } from '../../components/LoadingSpinner';
+import { useTranslation } from '../../src/i18n';
 import api from '../../services/api';
 
 const TABLET_MIN_WIDTH = 768;
@@ -22,6 +23,7 @@ interface NotificationItem {
 }
 
 export default function AlertsScreen() {
+  const { t } = useTranslation();
   const router = useRouter();
   const { width } = useWindowDimensions();
   const isTablet = width >= TABLET_MIN_WIDTH;
@@ -54,7 +56,7 @@ export default function AlertsScreen() {
       );
       setItems(merged);
     } catch (err: any) {
-      setError(err.message || 'No se pudieron cargar las notificaciones');
+      setError(err.message || t('alerts.loadError'));
     } finally {
       setIsLoading(false);
     }
@@ -63,12 +65,12 @@ export default function AlertsScreen() {
   async function handleDelete(item: NotificationItem) {
     const key = `${item.scope}:${item.id}`;
     Alert.alert(
-      'Eliminar notificación',
-      `¿Eliminar la notificación de ${item.medicine_name || item.medicine_nregistro}?`,
+      t('alerts.delete'),
+      `${t('alerts.deleteConfirm')} ${item.medicine_name || item.medicine_nregistro}?`,
       [
-        { text: 'Cancelar', style: 'cancel' },
+        { text: t('alerts.cancel'), style: 'cancel' },
         {
-          text: 'Eliminar',
+          text: t('alerts.confirmDelete'),
           style: 'destructive',
           onPress: async () => {
             setDeletingId(key);
@@ -78,7 +80,7 @@ export default function AlertsScreen() {
               });
               setItems(prev => prev.filter(i => !(i.scope === item.scope && i.id === item.id)));
             } catch (err: any) {
-              Alert.alert('Error', err.message || 'No se pudo eliminar');
+              Alert.alert('Error', err.message || t('alerts.deleteError'));
             } finally {
               setDeletingId(null);
             }
@@ -105,8 +107,8 @@ export default function AlertsScreen() {
               />
               <Text style={[styles.chipText, { color: colors.onPrimaryContainer }]}>
                 {item.scope === 'pharmacy'
-                  ? item.pharmacy_name || `Farmacia #${item.pharmacy_id}`
-                  : 'Cualquier farmacia'}
+                  ? item.pharmacy_name || `${t('alerts.pharmacy')} #${item.pharmacy_id}`
+                  : t('alerts.anyPharmacy')}
               </Text>
             </View>
             {item.pharmacy_address && (
@@ -132,22 +134,22 @@ export default function AlertsScreen() {
   }
 
   if (isLoading || authLoading) {
-    return <LoadingSpinner message="Cargando notificaciones..." />;
+    return <LoadingSpinner message={t('alerts.loading')} />;
   }
 
   if (!isAuthenticated) {
     return (
       <View style={[styles.container, styles.centered, { backgroundColor: colors.background }]}>
         <Ionicons name="lock-closed-outline" size={64} color={colors.border} />
-        <Text style={[styles.loginTitle, { color: colors.text }]}>Inicia sesión para continuar</Text>
+        <Text style={[styles.loginTitle, { color: colors.text }]}>{t('alerts.loginRequired')}</Text>
         <Text style={[styles.loginSubtitle, { color: colors.textSecondary }]}>
-          Necesitas estar autenticado para ver tus notificaciones
+          {t('alerts.loginDescription')}
         </Text>
         <TouchableOpacity
           style={[styles.loginButton, { backgroundColor: colors.primary }]}
           onPress={() => router.push('/auth/login')}
         >
-          <Text style={[styles.loginButtonText, { color: colors.onPrimaryContainer }]}>Iniciar Sesión</Text>
+          <Text style={[styles.loginButtonText, { color: colors.onPrimaryContainer }]}>{t('alerts.loginBtn')}</Text>
         </TouchableOpacity>
       </View>
     );
@@ -156,9 +158,9 @@ export default function AlertsScreen() {
   return (
     <View style={[styles.container, { backgroundColor: colors.background }]}>
       <View style={[styles.header, isTablet && styles.headerTablet]}>
-        <Text style={[styles.title, isTablet && styles.titleTablet, { color: colors.text }]}>Notificaciones Guardadas</Text>
+        <Text style={[styles.title, isTablet && styles.titleTablet, { color: colors.text }]}>{t('alerts.title')}</Text>
         <Text style={[styles.subtitle, isTablet && styles.subtitleTablet, { color: colors.textSecondary }]}>
-          Recibe avisos cuando medicamentos sin stock se repongan
+          {t('alerts.description')}
         </Text>
       </View>
 
@@ -166,7 +168,7 @@ export default function AlertsScreen() {
         <View style={[styles.errorContainer, isTablet && styles.errorContainerTablet, { backgroundColor: colors.dangerContainer }]}>
           <Text style={[styles.errorText, { color: colors.danger }]}>{error}</Text>
           <TouchableOpacity onPress={loadNotifications} style={styles.retryButton}>
-            <Text style={[styles.retryText, { color: colors.primary }]}>Reintentar</Text>
+            <Text style={[styles.retryText, { color: colors.primary }]}>{t('alerts.retry')}</Text>
           </TouchableOpacity>
         </View>
       )}
@@ -174,9 +176,9 @@ export default function AlertsScreen() {
       {!error && items.length === 0 && (
         <View style={styles.emptyContainer}>
           <Ionicons name="notifications-off-outline" size={isTablet ? 80 : 64} color={colors.border} />
-          <Text style={[styles.emptyTitle, isTablet && styles.emptyTitleTablet, { color: colors.text }]}>Sin notificaciones</Text>
+          <Text style={[styles.emptyTitle, isTablet && styles.emptyTitleTablet, { color: colors.text }]}>{t('alerts.empty')}</Text>
           <Text style={[styles.emptyText, isTablet && styles.emptyTextTablet, { color: colors.textSecondary }]}>
-            Toca la campana en una farmacia sin stock para recibir notificaciones cuando se reponga.
+            {t('alerts.emptyDescription')}
           </Text>
         </View>
       )}