feat: Integrate Expo mobile application into monorepo (#16)

- Add mobile/ directory with Expo React Native project
- Create API client with JWT auth and token refresh using AsyncStorage
- Implement AuthContext for login/register/logout flow
- Add screens: Login, Register, Library, Search, Settings
- Set up React Navigation with AuthStack and MainTabs
- Create packages/shared/ with shared types and utilities
- Add shared validation utilities (email, password strength)
- Update root package.json workspaces to include mobile + shared
- Add spec document docs/backend/009-expo-integration.md

mobile/src/api/annotations.ts

@@ -0,0 +1,55 @@
+import api from "./client";
+import type {
+  Bookmark,
+  Note,
+  CreateBookmarkPayload,
+  CreateNotePayload,
+  PaginatedResponse,
+} from "@cloud-reader/shared";
+
+export function fetchBookmarks(
+  bookId?: string,
+): Promise<PaginatedResponse<Bookmark>> {
+  const params = bookId ? { book: bookId } : {};
+  return api
+    .get<PaginatedResponse<Bookmark>>("/api/annotations/bookmarks/", { params })
+    .then((res) => res.data);
+}
+
+export function createBookmark(
+  payload: CreateBookmarkPayload,
+): Promise<Bookmark> {
+  return api
+    .post<Bookmark>("/api/annotations/bookmarks/", payload)
+    .then((res) => res.data);
+}
+
+export function deleteBookmark(id: string): Promise<void> {
+  return api.delete(`/api/annotations/bookmarks/${id}/`).then(() => {});
+}
+
+export function fetchNotes(bookId?: string): Promise<PaginatedResponse<Note>> {
+  const params = bookId ? { book: bookId } : {};
+  return api
+    .get<PaginatedResponse<Note>>("/api/annotations/notes/", { params })
+    .then((res) => res.data);
+}
+
+export function createNote(payload: CreateNotePayload): Promise<Note> {
+  return api
+    .post<Note>("/api/annotations/notes/", payload)
+    .then((res) => res.data);
+}
+
+export function updateNote(
+  id: string,
+  content: string,
+): Promise<Note> {
+  return api
+    .patch<Note>(`/api/annotations/notes/${id}/`, { content })
+    .then((res) => res.data);
+}
+
+export function deleteNote(id: string): Promise<void> {
+  return api.delete(`/api/annotations/notes/${id}/`).then(() => {});
+}