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

.gitignore

@@ -0,0 +1,34 @@
+# Python
+__pycache__/
+*.py[cod]
+*.egg-info/
+dist/
+*.egg
+.venv/
+venv/
+*.sqlite3
+
+# Node
+node_modules/
+dist/
+build/
+.yarn/
+yarn-error.log
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Environment
+.env
+.env.local
+.env.production
+
+# Build artifacts (generated)
+frontend/dist/