feat: bookmarks and notes management

- Backend: Django REST Framework API with Bookmark and Note models
  - ViewSets with user-scoped querysets and select_related for N+1 prevention
  - Create/List/Detail/Update/Delete endpoints
  - Batch delete operations
  - Unique constraint on user+book+page for bookmarks
  - IsOwner permission class for object-level access control
  - Full serializer validation (page > 0, non-empty content, duplicate check)
  - 30+ pytest-django tests covering CRUD, auth, filtering, edge cases

- Frontend: React TypeScript components
  - AnnotationsContext with useReducer for state management
  - BookmarkList, NoteList, AddAnnotationForm, AnnotationsDashboard
  - Inline note editing with immediate save
  - Batch delete support
  - API client with JWT auto-refresh interceptors
  - Paginated query hook for infinite scroll support
  - Responsive CSS with loading/empty states

- Infrastructure: Django project with custom User model, JWT auth, CORS
  - PostgreSQL database models with proper FK and indexes
  - Django admin configuration for all models

backend/apps/books/views.py

@@ -0,0 +1,24 @@
+from django_filters.rest_framework import DjangoFilterBackend
+from rest_framework import viewsets
+from rest_framework.filters import OrderingFilter, SearchFilter
+from rest_framework.permissions import IsAuthenticated
+
+from apps.books.models import Book
+from apps.books.serializers import BookListSerializer, BookSerializer
+
+
+class BookViewSet(viewsets.ModelViewSet):
+    """CRUD for books."""
+
+    queryset = Book.objects.all()
+    permission_classes = [IsAuthenticated]
+    filter_backends = [DjangoFilterBackend, SearchFilter, OrderingFilter]
+    filterset_fields = ["author"]
+    search_fields = ["title", "author"]
+    ordering_fields = ["title", "author", "created_at"]
+    ordering = ["title"]
+
+    def get_serializer_class(self):
+        if self.action == "list":
+            return BookListSerializer
+        return BookSerializer