feat: bookmarks and notes management

- Backend: Django REST Framework API with Bookmark and Note models
  - ViewSets with user-scoped querysets and select_related for N+1 prevention
  - Create/List/Detail/Update/Delete endpoints
  - Batch delete operations
  - Unique constraint on user+book+page for bookmarks
  - IsOwner permission class for object-level access control
  - Full serializer validation (page > 0, non-empty content, duplicate check)
  - 30+ pytest-django tests covering CRUD, auth, filtering, edge cases

- Frontend: React TypeScript components
  - AnnotationsContext with useReducer for state management
  - BookmarkList, NoteList, AddAnnotationForm, AnnotationsDashboard
  - Inline note editing with immediate save
  - Batch delete support
  - API client with JWT auto-refresh interceptors
  - Paginated query hook for infinite scroll support
  - Responsive CSS with loading/empty states

- Infrastructure: Django project with custom User model, JWT auth, CORS
  - PostgreSQL database models with proper FK and indexes
  - Django admin configuration for all models

web/src/App.tsx

@@ -0,0 +1,46 @@
+/**
+ * App — root component with simple page navigation (library ↔ book detail).
+ */
+
+import { useState, lazy, Suspense } from "react";
+import "./App.css";
+
+const LibraryPage = lazy(() => import("./pages/LibraryPage"));
+const BookDetailPage = lazy(() => import("./pages/BookDetailPage"));
+
+type View =
+  | { kind: "library" }
+  | { kind: "detail"; bookId: number };
+
+function LoadingFallback() {
+  return (
+    <div className="loading-spinner">
+      <div className="spinner" />
+      <p>Loading...</p>
+    </div>
+  );
+}
+
+export default function App() {
+  const [view, setView] = useState<View>({ kind: "library" });
+
+  const handleBookSelect = (id: number) => {
+    setView({ kind: "detail", bookId: id });
+  };
+
+  const handleBack = () => {
+    setView({ kind: "library" });
+  };
+
+  return (
+    <div className="app">
+      <Suspense fallback={<LoadingFallback />}>
+        {view.kind === "library" ? (
+          <LibraryPage onBookSelect={handleBookSelect} />
+        ) : (
+          <BookDetailPage bookId={view.bookId} onBack={handleBack} />
+        )}
+      </Suspense>
+    </div>
+  );
+}