feat(env): Update environment configuration and enhance email functionality

- Renamed DATABASE_URL to POSTGRES_URL in .env.example for clarity.
- Added SMTP configuration for email sending, including host, port, user, password, and from address.
- Updated package.json to include new dependencies for email handling and UI components.
- Modified middleware to handle public and protected routes more effectively.
- Enhanced API routes for studies to support user roles and permissions.
- Updated database schema to include invitations and user roles related to studies.
- Improved user permissions handling in the permissions module.
- Added new utility functions for managing user roles and study access.

.env.example

@@ -3,11 +3,18 @@ NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY=pk_test_
 CLERK_SECRET_KEY=sk_test_
 
 # Database
-DATABASE_URL="postgresql://user:password@localhost:5432/dbname"
+POSTGRES_URL="postgresql://user:password@localhost:5432/dbname"
 
 # Next.js
 NEXT_PUBLIC_APP_URL="http://localhost:3000"
 
+# Email (SMTP)
+SMTP_HOST=smtp.mail.me.com
+SMTP_PORT=587
+SMTP_USER=your-email@example.com
+SMTP_PASSWORD=your-app-specific-password
+SMTP_FROM_ADDRESS=noreply@yourdomain.com
+
 # Optional: For production deployments
 # NEXT_PUBLIC_APP_URL="https://yourdomain.com"
 # VERCEL_URL="https://yourdomain.com"