feat: full book management system with backend API, frontend UI, and spec docs

- Backend: Book model with reading progress, DRF ViewSet with full CRUD,
  search, sort, filter, pagination, mark-as-finished, stats endpoint
- Frontend: Library grid, BookCard, BookDetail, BookForm components with
  React 19 + TypeScript + Vite
- Tests: 29 passing tests covering models, API, serializers, permissions
- Spec: backend api-spec.md and frontend component-spec.md in docs/

Closes crisleo-hermes/cloud-reader#3

backend/books/urls.py

@@ -0,0 +1,13 @@
+from __future__ import annotations
+
+from django.urls import include, path
+from rest_framework.routers import DefaultRouter
+
+from books.views import BookViewSet
+
+router = DefaultRouter()
+router.register(r"books", BookViewSet, basename="book")
+
+urlpatterns = [
+    path("", include(router.urls)),
+]