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/api/annotations.ts

@@ -0,0 +1,96 @@
+import api from "@/api/client";
+import type {
+  Bookmark,
+  CreateBookmarkPayload,
+  Note,
+  CreateNotePayload,
+  UpdateNotePayload,
+  PaginatedResponse,
+} from "@/types";
+
+/** Fetch bookmarks for the current user, optionally filtered by book */
+export async function fetchBookmarks(
+  bookId?: string
+): Promise<PaginatedResponse<Bookmark>> {
+  const params: Record<string, string> = {};
+  if (bookId) params.book = bookId;
+  const { data } = await api.get<PaginatedResponse<Bookmark>>(
+    "/annotations/bookmarks/",
+    { params }
+  );
+  return data;
+}
+
+/** Create a new bookmark */
+export async function createBookmark(
+  payload: CreateBookmarkPayload
+): Promise<Bookmark> {
+  const { data } = await api.post<Bookmark>(
+    "/annotations/bookmarks/",
+    payload
+  );
+  return data;
+}
+
+/** Delete a bookmark by id */
+export async function deleteBookmark(id: string): Promise<void> {
+  await api.delete(`/annotations/bookmarks/${id}/`);
+}
+
+/** Batch delete bookmarks */
+export async function batchDeleteBookmarks(
+  ids: string[]
+): Promise<{ deleted: number }> {
+  const { data } = await api.delete<{ deleted: number }>(
+    "/annotations/bookmarks/batch-delete/",
+    { data: { ids } }
+  );
+  return data;
+}
+
+/** Fetch notes for the current user, optionally filtered by book */
+export async function fetchNotes(
+  bookId?: string
+): Promise<PaginatedResponse<Note>> {
+  const params: Record<string, string> = {};
+  if (bookId) params.book = bookId;
+  const { data } = await api.get<PaginatedResponse<Note>>(
+    "/annotations/notes/",
+    { params }
+  );
+  return data;
+}
+
+/** Create a new note */
+export async function createNote(payload: CreateNotePayload): Promise<Note> {
+  const { data } = await api.post<Note>("/annotations/notes/", payload);
+  return data;
+}
+
+/** Update a note's content */
+export async function updateNote(
+  id: string,
+  payload: UpdateNotePayload
+): Promise<Note> {
+  const { data } = await api.patch<Note>(
+    `/annotations/notes/${id}/`,
+    payload
+  );
+  return data;
+}
+
+/** Delete a note by id */
+export async function deleteNote(id: string): Promise<void> {
+  await api.delete(`/annotations/notes/${id}/`);
+}
+
+/** Batch delete notes */
+export async function batchDeleteNotes(
+  ids: string[]
+): Promise<{ deleted: number }> {
+  const { data } = await api.delete<{ deleted: number }>(
+    "/annotations/notes/batch-delete/",
+    { data: { ids } }
+  );
+  return data;
+}