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.

backend/utils/push_sender.py

@@ -0,0 +1,68 @@
+import json
+import logging
+import os
+
+from pywebpush import webpush, WebPushException
+
+from db.push_subscriptions import get_subscriptions_by_user, delete_subscription_by_id
+
+logger = logging.getLogger(__name__)
+
+
+def _get_vapid_private_key() -> str | None:
+    return os.environ.get('VAPID_PRIVATE_KEY')
+
+
+def _get_vapid_claims_email() -> str:
+    return os.environ.get('VAPID_CLAIMS_EMAIL', 'admin@reward-app.local')
+
+
+def send_push_to_user(user_id: str, payload: dict) -> int:
+    """
+    Send a web push notification to all stored subscriptions for the user.
+    Returns the number of subscriptions successfully notified.
+
+    Stale/expired subscriptions (HTTP 404/410) are removed automatically.
+    """
+    private_key = _get_vapid_private_key()
+    if not private_key:
+        logger.warning('VAPID_PRIVATE_KEY not configured; skipping push notification')
+        return 0
+
+    subscriptions = get_subscriptions_by_user(user_id)
+    if not subscriptions:
+        return 0
+
+    claims_email = _get_vapid_claims_email()
+    sent = 0
+
+    for sub in subscriptions:
+        try:
+            subscription_info = {
+                'endpoint': sub.endpoint,
+                'keys': sub.keys,
+            }
+            webpush(
+                subscription_info=subscription_info,
+                data=json.dumps(payload),
+                vapid_private_key=private_key,
+                vapid_claims={'sub': f'mailto:{claims_email}'},
+                ttl=86400,
+            )
+            sent += 1
+        except WebPushException as e:
+            status_code = e.response.status_code if e.response is not None else None
+            if status_code in (404, 410):
+                # Subscription is gone — clean it up
+                logger.info(
+                    f'Removing stale push subscription {sub.id} for user {user_id} (HTTP {status_code})'
+                )
+                delete_subscription_by_id(sub.id)
+            else:
+                logger.error(
+                    f'WebPushException for subscription {sub.id} (user {user_id}): {e}'
+                )
+        except Exception as e:
+            logger.error(f'Unexpected error sending push to subscription {sub.id}: {e}')
+
+    return sent