Add Next.js adapter API for auth lib

[SOG-web]

Description

Create a comprehensive Next.js adapter API for the auth library.

Tasks

• Create Next.js specific middleware
• Implement Next.js API route handlers for auth endpoints
• Add support for both Pages Router and App Router
• Create Next.js specific session management
• Implement Next.js specific guards/middleware for protected routes
• Add configuration options for Next.js integration
• Create examples for common Next.js use cases
• Document Next.js adapter usage

Acceptance Criteria

• Next.js adapter works seamlessly with the auth library
• API is intuitive and follows Next.js conventions
• Support for both Pages Router and App Router
• Examples cover common use cases
• Documentation is comprehensive