Add push notification functionality with tests and digest scheduler

- Implemented push subscription API with tests for subscribing and unsubscribing users.
- Created web push notification tests triggered by child actions.
- Added digest scheduler to send email digests to users at 9 PM local time.
- Developed utility functions for creating and validating digest action tokens.
- Integrated web push sender to handle sending notifications to users.
- Added service worker for handling push notifications in the frontend.
- Created a push opt-in component for user notification preferences.
- Implemented tests for the push opt-in component to ensure correct behavior.
- Updated frontend services to manage push subscriptions and permissions.

frontend/vue-app/public/sw.js

@@ -0,0 +1,68 @@
+/* Service Worker for Reward App push notifications */
+
+self.addEventListener('push', function (event) {
+  if (!event.data) return
+
+  let payload
+  try {
+    payload = event.data.json()
+  } catch (e) {
+    payload = { title: 'Reward App', body: event.data.text() }
+  }
+
+  const title = payload.title || 'Reward App'
+  const options = {
+    body: payload.body || '',
+    data: payload,
+    actions: [
+      { action: 'approve', title: 'Approve' },
+      { action: 'deny', title: 'Deny' },
+    ],
+  }
+
+  event.waitUntil(self.registration.showNotification(title, options))
+})
+
+self.addEventListener('notificationclick', function (event) {
+  event.notification.close()
+
+  const payload = event.notification.data || {}
+  const approveToken = payload.approve_token
+  const denyToken = payload.deny_token
+  const childId = payload.child_id
+  const entityId = payload.entity_id
+  const entityType = payload.entity_type
+
+  if (event.action === 'approve' && approveToken) {
+    event.waitUntil(fetch('/api/digest-action/' + approveToken))
+    return
+  }
+
+  if (event.action === 'deny' && denyToken) {
+    event.waitUntil(fetch('/api/digest-action/' + denyToken))
+    return
+  }
+
+  // Body tap — open or focus the app then navigate to the deep link
+  const deepLinkUrl =
+    childId && entityId && entityType
+      ? '/parent/' + childId + '?scrollTo=' + entityId + '&entityType=' + entityType
+      : '/parent'
+
+  event.waitUntil(
+    clients.matchAll({ type: 'window', includeUncontrolled: true }).then(function (clientList) {
+      const sameOriginClients = clientList.filter(function (c) {
+        return new URL(c.url).origin === self.location.origin
+      })
+
+      if (sameOriginClients.length > 0) {
+        const client = sameOriginClients[0]
+        return client.focus().then(function () {
+          return client.navigate(deepLinkUrl)
+        })
+      }
+
+      return clients.openWindow(deepLinkUrl)
+    }),
+  )
+})