Notifications System Integration

I'm looking to enhance my WordPress and Next.js website with a robust notifications bar. This feature should allow users to customize alerts, both on-site and via email.

Key Notifications:
- Demand posted alerts (categories to be defined)
- New proposal notifications
- Proposal status updates (accepted, rejected, completed)

Additionally, I need assistance with ensuring mobile responsiveness for this feature.

Ideal skills and experience:
- Proficiency in WordPress and Next.js
- Strong PHP knowledge
- Experience with implementing custom notification systems
- Mobile responsiveness expertise

Please provide examples of similar work done.