Draft: Resolve "Reminder Message for Volunteers to Claim Certificates"

Description: Added Certificate Reminder System to send notifications to volunteers who haven't claimed their certificates.

Type of Change:

• Feature Development

Features Added:

• Certificate Management dashboard for admins at /certificate-management
• Multi-channel notifications: Email, WhatsApp, and In-App
• Real-time notifications via Socket.io with NotificationBell component
• Track certificate status (task_completed, certificate_generated, certificate_claimed)
• Send individual or bulk reminders to volunteers
• 

New Files:

• backend/socket.js - Socket.io real-time notifications
• backend/routes/certificateRoutes.js - Certificate management API
• backend/routes/notificationRoutes.js - Notification API
• backend/utils/notificationService.js - Email, WhatsApp, In-App service
• frontend/src/Pages/CertificateManagement.jsx - Admin dashboard
• frontend/src/Components/NotificationBell.jsx - Notification bell in navbar
• docs/certificate_reminder_system.md - Documentation
• CERTIFICATE_SETUP.md - Setup guide

Configuration Required: Add to backend/.env:

• EMAIL_USER, EMAIL_PASSWORD (Gmail App Password)
• TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN, TWILIO_WHATSAPP_NUMBER

See CERTIFICATE_SETUP.md for full setup instructions.

Testing:

• Tested on desktop
• Tested email sending
• Tested WhatsApp sending
• Tested in-app notifications