refactor: consolidate backend/frontend, remove api/web duplicates

- backend/ kept as canonical, api/ features merged (EBook, ReadingProgress, ReadingSettings)
- frontend/ kept as canonical, web/ pages merged (Library, Reader, AddBook, Auth, Settings)
- Added Dockerfiles for backend/ and frontend/
- Updated docker-compose.yml for consolidated services
- Updated README, package.json workspaces
- api/ and web/ directories removed

backend/requirements.txt

@@ -8,6 +8,7 @@ pydantic==2.10.5
 pydantic-settings==2.7.1
 python-dotenv==1.0.1
 gunicorn==23.0.0
+Pillow>=11.0.0
 pytest==8.3.4
 pytest-django==4.9.0
 pytest-cov==6.0.0