Implement Django REST Framework for API Development

Convert the existing Django backend into a REST API using Django REST Framework (DRF).

Tasks:

• Install djangorestframework and add to requirements.txt
• Configure DRF in Django settings
• Create serializers for Book and BookChunk models
• Implement API viewsets for models
• Set up API routing with DRF router
• Add API documentation using drf-spectacular or drf-yasg
• Create basic API endpoints:
  • GET /api/books/ - List all books
  • GET /api/books/{id}/ - Get specific book details
  • GET /api/books/{id}/chunks/ - Get book chunks