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/requirements.txt

@@ -0,0 +1,14 @@
+Django==5.1.7
+djangorestframework==3.15.2
+djangorestframework-simplejwt==5.4.0
+django-filter==25.1
+django-cors-headers==4.6.0
+psycopg2-binary==2.9.10
+pydantic==2.10.5
+pydantic-settings==2.7.1
+python-dotenv==1.0.1
+gunicorn==23.0.0
+pytest==8.3.4
+pytest-django==4.9.0
+pytest-cov==6.0.0
+coverage==7.6.10