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

frontend/src/hooks/index.ts

@@ -0,0 +1 @@
+export { usePaginatedQuery } from "./usePaginatedQuery";

frontend/src/hooks/usePaginatedQuery.ts

@@ -0,0 +1,69 @@
+import { useState, useCallback, useRef, useEffect } from "react";
+import type { PaginatedResponse } from "@/types";
+
+interface UsePaginatedQueryOptions<T> {
+  fetchFn: (cursor?: string) => Promise<PaginatedResponse<T>>;
+}
+
+interface UsePaginatedQueryResult<T> {
+  items: T[];
+  loading: boolean;
+  error: string | null;
+  hasMore: boolean;
+  loadMore: () => Promise<void>;
+  refresh: () => Promise<void>;
+}
+
+/**
+ * Hook for paginated list fetching with infinite scroll support.
+ */
+export function usePaginatedQuery<T>({
+  fetchFn,
+}: UsePaginatedQueryOptions<T>): UsePaginatedQueryResult<T> {
+  const [items, setItems] = useState<T[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [nextCursor, setNextCursor] = useState<string | null>(null);
+  const loadingRef = useRef(false);
+
+  const refresh = useCallback(async () => {
+    setLoading(true);
+    setError(null);
+    try {
+      const response = await fetchFn();
+      setItems(response.results);
+      setNextCursor(response.next);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to fetch data");
+    } finally {
+      setLoading(false);
+    }
+  }, [fetchFn]);
+
+  const loadMore = useCallback(async () => {
+    if (!nextCursor || loadingRef.current) return;
+    loadingRef.current = true;
+    try {
+      const response = await fetchFn(nextCursor);
+      setItems((prev) => [...prev, ...response.results]);
+      setNextCursor(response.next);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to load more");
+    } finally {
+      loadingRef.current = false;
+    }
+  }, [nextCursor, fetchFn]);
+
+  useEffect(() => {
+    refresh();
+  }, [refresh]);
+
+  return {
+    items,
+    loading,
+    error,
+    hasMore: nextCursor !== null,
+    loadMore,
+    refresh,
+  };
+}