feat: add Expo Push notifications for mobile and configure EXPO_ACCESS_TOKEN

- Backend: add expo_push_tokens table, expo-register/unregister endpoints, hybrid VAPID+Expo push sender
- Mobile: register Expo push token on app launch, bell toggle on medicine/pharmacy detail screens
- .env.example: document EXPO_ACCESS_TOKEN configuration
- Dark mode hover fixes for search suggestions and recent buttons

apps/frontend-mobile/app/pharmacy/[id].tsx

@@ -4,6 +4,8 @@ import { useLocalSearchParams, useRouter } from 'expo-router';
 import { Ionicons } from '@expo/vector-icons';
 import MapView, { Marker } from 'react-native-maps';
 import { getPharmacy, getPharmacyMedicines } from '../../services/pharmacies';
+import { subscribeToMedicine, unsubscribeFromMedicine } from '../../services/notifications';
+import { useAuth } from '../../hooks/useAuth';
 import { LoadingSpinner } from '../../components/LoadingSpinner';
 import { useThemeContext } from '../../components/ThemeProvider';
 import { spacing, borderRadius } from '../../constants/theme';
@@ -13,9 +15,11 @@ export default function PharmacyDetailScreen() {
   const { id } = useLocalSearchParams<{ id: string }>();
   const router = useRouter();
   const { colors } = useThemeContext();
+  const { isAuthenticated } = useAuth();
   const [pharmacy, setPharmacy] = useState<Pharmacy | null>(null);
   const [medicines, setMedicines] = useState<PharmacyMedicine[]>([]);
   const [isLoading, setIsLoading] = useState(true);
+  const [subscribedMeds, setSubscribedMeds] = useState<Set<string>>(new Set());
 
   useEffect(() => {
     if (!id) return;
@@ -51,6 +55,27 @@ export default function PharmacyDetailScreen() {
     }
   };
 
+  const handleToggleMedSubscription = async (nregistro: string, medicineName: string) => {
+    if (!isAuthenticated) return;
+    const key = nregistro;
+    const isSub = subscribedMeds.has(key);
+    try {
+      if (isSub) {
+        await unsubscribeFromMedicine(nregistro, Number(id));
+        setSubscribedMeds(prev => {
+          const next = new Set(prev);
+          next.delete(key);
+          return next;
+        });
+      } else {
+        await subscribeToMedicine(nregistro, medicineName, Number(id));
+        setSubscribedMeds(prev => new Set(prev).add(key));
+      }
+    } catch {
+      // silently fail
+    }
+  };
+
   if (isLoading) {
     return <LoadingSpinner message="Cargando farmacia..." />;
   }
@@ -124,22 +149,41 @@ export default function PharmacyDetailScreen() {
         {medicines.length === 0 ? (
           <Text style={[styles.noMedicines, { color: colors.textSecondary }]}>No hay medicamentos disponibles</Text>
         ) : (
-          medicines.map((med) => (
-            <TouchableOpacity
-              key={med.id}
-              style={[styles.medicineCard, { backgroundColor: colors.card }]}
-              onPress={() => router.push(`/medicine/${med.medicine_nregistro}`)}
-            >
-              <View style={styles.medicineInfo}>
-                <Text style={[styles.medicineName, { color: colors.text }]}>{med.medicine_name}</Text>
-                <Text style={[styles.medicineNregistro, { color: colors.textSecondary }]}>Reg: {med.medicine_nregistro}</Text>
+          medicines.map((med) => {
+            const isSub = subscribedMeds.has(med.medicine_nregistro);
+            return (
+              <View key={med.id} style={[styles.medicineCard, { backgroundColor: colors.card }]}>
+                <TouchableOpacity
+                  style={styles.medicineCardContent}
+                  onPress={() => router.push(`/medicine/${med.medicine_nregistro}`)}
+                >
+                  <View style={styles.medicineInfo}>
+                    <Text style={[styles.medicineName, { color: colors.text }]}>{med.medicine_name}</Text>
+                    <Text style={[styles.medicineNregistro, { color: colors.textSecondary }]}>Reg: {med.medicine_nregistro}</Text>
+                  </View>
+                  <View style={styles.medicineStock}>
+                    <Text style={[styles.price, { color: colors.primary }]}>{med.price.toFixed(2)} €</Text>
+                    <Text style={[styles.stock, { color: colors.textSecondary }]}>Stock: {med.stock}</Text>
+                  </View>
+                </TouchableOpacity>
+                {isAuthenticated && (
+                  <TouchableOpacity
+                    style={[styles.bellButton, { backgroundColor: isSub ? colors.primary : colors.surfaceVariant, borderTopColor: colors.border }]}
+                    onPress={() => handleToggleMedSubscription(med.medicine_nregistro, med.medicine_name)}
+                  >
+                    <Ionicons
+                      name={isSub ? 'notifications' : 'notifications-outline'}
+                      size={18}
+                      color={isSub ? '#fff' : colors.textSecondary}
+                    />
+                    <Text style={[styles.bellText, { color: isSub ? '#fff' : colors.textSecondary }]}>
+                      {isSub ? 'Notificaciones activas' : 'Notificarme cuando haya stock'}
+                    </Text>
+                  </TouchableOpacity>
+                )}
               </View>
-              <View style={styles.medicineStock}>
-                <Text style={[styles.price, { color: colors.primary }]}>{med.price.toFixed(2)} €</Text>
-                <Text style={[styles.stock, { color: colors.textSecondary }]}>Stock: {med.stock}</Text>
-              </View>
-            </TouchableOpacity>
-          ))
+            );
+          })
         )}
       </View>
     </ScrollView>
@@ -207,11 +251,14 @@ const styles = StyleSheet.create({
     padding: spacing.xl,
   },
   medicineCard: {
+    borderRadius: borderRadius.md,
+    marginBottom: spacing.sm,
+    overflow: 'hidden',
+  },
+  medicineCardContent: {
     flexDirection: 'row',
     justifyContent: 'space-between',
-    borderRadius: borderRadius.md,
     padding: spacing.md,
-    marginBottom: spacing.sm,
   },
   medicineInfo: {
     flex: 1,
@@ -235,6 +282,18 @@ const styles = StyleSheet.create({
     fontSize: 12,
     marginTop: spacing.xs,
   },
+  bellButton: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    justifyContent: 'center',
+    gap: spacing.xs,
+    paddingVertical: spacing.sm,
+    borderTopWidth: 1,
+  },
+  bellText: {
+    fontSize: 13,
+    fontWeight: '600',
+  },
   errorContainer: {
     flex: 1,
     justifyContent: 'center',