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/Dockerfile

@@ -0,0 +1,18 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    libpq-dev gcc && \
+    rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt ./
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . ./
+
+RUN mkdir -p media
+
+EXPOSE 8000
+
+CMD ["python", "manage.py", "runserver", "0.0.0.0:8000"]