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/services/notifications.ts

@@ -2,6 +2,7 @@ import * as Notifications from 'expo-notifications';
 import * as Device from 'expo-device';
 import * as Constants from 'expo-constants';
 import { Platform } from 'react-native';
+import api from './api';
 
 Notifications.setNotificationHandler({
   handleNotification: async () => ({
@@ -12,6 +13,8 @@ Notifications.setNotificationHandler({
   }),
 });
 
+let _cachedToken: string | null = null;
+
 export async function registerForPushNotifications() {
   if (!Device.isDevice) {
     console.log('Push notifications require a physical device');
@@ -48,6 +51,11 @@ export async function registerForPushNotifications() {
       projectId,
     });
 
+    _cachedToken = token.data;
+
+    // Register token with backend (fire and forget)
+    registerTokenWithBackend(token.data).catch(() => {});
+
     return token.data;
   } catch (e) {
     console.log('Error getting push token:', e);
@@ -55,6 +63,52 @@ export async function registerForPushNotifications() {
   }
 }
 
+async function registerTokenWithBackend(token: string) {
+  try {
+    await api.post('/notifications/expo-register', { token });
+  } catch (e) {
+    console.log('Failed to register push token with backend:', e);
+  }
+}
+
+export async function subscribeToMedicine(
+  medicineNregistro: string,
+  medicineName: string | null,
+  pharmacyId?: number | null
+) {
+  const token = _cachedToken;
+  if (!token) {
+    console.log('No push token available for subscription');
+    return;
+  }
+  try {
+    await api.post('/notifications/expo-register', {
+      token,
+      medicine_nregistro: medicineNregistro,
+      medicine_name: medicineName,
+      pharmacy_id: pharmacyId || null,
+    });
+  } catch (e) {
+    console.log('Failed to subscribe to medicine notifications:', e);
+  }
+}
+
+export async function unsubscribeFromMedicine(
+  medicineNregistro: string,
+  pharmacyId?: number | null
+) {
+  try {
+    await api.delete('/notifications/expo-unregister', {
+      data: {
+        medicine_nregistro: medicineNregistro,
+        pharmacy_id: pharmacyId || null,
+      },
+    });
+  } catch (e) {
+    console.log('Failed to unsubscribe from medicine notifications:', e);
+  }
+}
+
 export async function scheduleMedicineAvailabilityNotification(
   medicineName: string,
   pharmacyName: string