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/api/push_subscription_api.py

@@ -0,0 +1,59 @@
+from flask import Blueprint, request, jsonify, current_app
+from tinydb import Query
+
+from api.utils import get_validated_user_id
+from db.push_subscriptions import upsert_subscription, delete_by_endpoint
+from db.db import users_db
+
+push_subscription_api = Blueprint('push_subscription_api', __name__)
+
+
+@push_subscription_api.route('/push-vapid-key', methods=['GET'])
+def get_vapid_public_key():
+    """Return the VAPID public key for the frontend to use when subscribing."""
+    public_key = current_app.config.get('VAPID_PUBLIC_KEY', '')
+    return jsonify({'public_key': public_key}), 200
+
+
+@push_subscription_api.route('/push-subscription', methods=['POST'])
+def subscribe():
+    """Upsert a push subscription for the current user."""
+    user_id = get_validated_user_id()
+    if not user_id:
+        return jsonify({'error': 'Unauthorized', 'code': 'UNAUTHORIZED'}), 401
+
+    data = request.get_json() or {}
+    endpoint = data.get('endpoint')
+    keys = data.get('keys')
+    timezone_str = data.get('timezone')
+
+    if not endpoint or not isinstance(keys, dict):
+        return jsonify({'error': 'endpoint and keys are required', 'code': 'MISSING_FIELDS'}), 400
+    if 'p256dh' not in keys or 'auth' not in keys:
+        return jsonify({'error': 'keys must contain p256dh and auth', 'code': 'MISSING_FIELDS'}), 400
+
+    sub = upsert_subscription(user_id=user_id, endpoint=endpoint, keys=keys)
+
+    # Update user timezone if provided
+    if timezone_str:
+        UserQ = Query()
+        users_db.update({'timezone': timezone_str}, UserQ.id == user_id)
+
+    return jsonify({'message': 'Subscription saved', 'id': sub.id}), 200
+
+
+@push_subscription_api.route('/push-subscription', methods=['DELETE'])
+def unsubscribe():
+    """Remove a push subscription for the current user by endpoint."""
+    user_id = get_validated_user_id()
+    if not user_id:
+        return jsonify({'error': 'Unauthorized', 'code': 'UNAUTHORIZED'}), 401
+
+    data = request.get_json() or {}
+    endpoint = data.get('endpoint')
+
+    if not endpoint:
+        return jsonify({'error': 'endpoint is required', 'code': 'MISSING_FIELDS'}), 400
+
+    removed = delete_by_endpoint(user_id=user_id, endpoint=endpoint)
+    return jsonify({'message': 'Subscription removed', 'removed': removed}), 200