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

frontend/Dockerfile

@@ -0,0 +1,12 @@
+FROM node:20-alpine
+
+WORKDIR /app
+
+COPY package.json yarn.lock ./
+RUN yarn install --frozen-lockfile
+
+COPY . ./
+
+EXPOSE 5173
+
+CMD ["yarn", "dev", "--host"]