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/src/components/notification/PushOptIn.vue

@@ -0,0 +1,91 @@
+<template>
+  <div v-if="showBanner" class="push-opt-in-banner" role="status" aria-live="polite">
+    <template v-if="permissionState === 'default'">
+      <span class="push-opt-in-text"
+        >Enable notifications to stay updated on chores and rewards.</span
+      >
+      <button class="btn btn-primary push-opt-in-btn" @click="onEnable">Enable</button>
+      <button class="push-opt-in-dismiss" @click="dismiss" aria-label="Dismiss">✕</button>
+    </template>
+    <template v-else-if="permissionState === 'denied'">
+      <span class="push-opt-in-text"
+        >Notifications are blocked. Enable them in your browser settings to receive alerts.</span
+      >
+      <button class="push-opt-in-dismiss" @click="dismiss" aria-label="Dismiss">✕</button>
+    </template>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, onMounted } from 'vue'
+import { subscribeToPush, getPushPermissionState } from '@/services/pushSubscription'
+
+const permissionState = ref<NotificationPermission | 'unsupported'>('default')
+const dismissed = ref(false)
+
+const showBanner = ref(false)
+
+onMounted(() => {
+  if (!('Notification' in window)) {
+    return
+  }
+  permissionState.value = Notification.permission
+  if (permissionState.value === 'granted') {
+    // Already granted — ensure subscription is registered silently
+    subscribeToPush()
+    return
+  }
+  showBanner.value = true
+})
+
+async function onEnable() {
+  const success = await subscribeToPush()
+  if (success) {
+    permissionState.value = 'granted'
+    showBanner.value = false
+  } else {
+    permissionState.value = Notification.permission as NotificationPermission
+  }
+}
+
+function dismiss() {
+  dismissed.value = true
+  showBanner.value = false
+}
+</script>
+
+<style scoped>
+.push-opt-in-banner {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  background: var(--list-item-bg, #f0f4ff);
+  border: 1px solid var(--btn-primary, #4a90e2);
+  border-radius: 8px;
+  padding: 0.6rem 1rem;
+  margin: 0.5rem 0;
+  font-size: 0.88rem;
+  flex-wrap: wrap;
+}
+
+.push-opt-in-text {
+  flex: 1;
+  min-width: 0;
+}
+
+.push-opt-in-btn {
+  font-size: 0.85rem;
+  padding: 0.35rem 0.9rem;
+  white-space: nowrap;
+}
+
+.push-opt-in-dismiss {
+  background: none;
+  border: none;
+  cursor: pointer;
+  color: var(--text-muted, #888);
+  font-size: 1rem;
+  padding: 0 0.25rem;
+  line-height: 1;
+}
+</style>