Address Reid's PR #25 review comments

🔴 Blocking fixes:
- Add reader app migration (apps/reader/migrations/0001_initial.py)
- Remove duplicate ReadingSettings from apps.books to resolve model clash
  with apps.reader.ReadingSettings (keep richer reader version)
- Redirect books serializers/views to use reader app's ReadingSettings
- Update frontend API endpoints to match main's backend routes:
  /api/books/ebooks/{id}/toc/ (chapters)
  /api/books/ebooks/{id}/content/?page=N (chapter content)
  /api/books/ebooks/{id}/progress/ (GET/PATCH progress)
- Add DOMPurify sanitization for dangerouslySetInnerHTML (XSS fix)

🟡 Non-blocking fixes:
- Fix CSS typo: landascape -> landscape in reader.css
- Add null-safe fallback for book.title in ReadingPage

backend/apps/books/urls.py

@@ -1,7 +1,7 @@
 from django.urls import include, path
 from rest_framework.routers import DefaultRouter
 
-from apps.books.views import BookViewSet, EBookViewSet, ReadingSettingsViewSet
+from apps.books.views import BookViewSet, EBookViewSet
 
 router = DefaultRouter()
 router.register(r"", BookViewSet, basename="book")
@@ -12,5 +12,4 @@ ebook_router.register(r"ebooks", EBookViewSet, basename="ebook")
 urlpatterns = [
     path("", include(router.urls)),
     path("", include(ebook_router.urls)),
-    path("settings/", ReadingSettingsViewSet.as_view({"get": "list", "patch": "partial_update"}), name="reading-settings"),
 ]