feat: monorepo structure with Django backend, React frontend, and Expo mobile app

- Backend: Django 5 + DRF with accounts, documents, collections, and reading apps
  - Custom User model with email-based auth, JWT via SimpleJWT
  - Full CRUD viewsets with ModelSerializer + DRF routers
  - pytest, Ruff, drf-spectacular (OpenAPI), whitenoise
  - Dockerfile for production deployment

- Frontend: React 18 + TypeScript + Vite
  - Lazy-loaded routes with ProtectedRoute/PublicRoute guards
  - Auth context with useReducer, token refresh interceptor
  - Pages: Login, Register, Library, Document Detail, Reader, Collections, Settings
  - Dark theme, responsive grid layout, Vite proxy to Django backend

- Mobile: Expo SDK 51 + React Native + Expo Router
  - File-based routing with login, register, and library screens
  - AsyncStorage for token persistence, token refresh interceptor
  - Shared API types via @cloud-reader/shared workspace package

- Shared: TypeScript types (API responses, auth, documents, etc.)
- CI/CD: 3 independent GitHub Actions pipelines (backend, frontend, mobile)

mobile/app/_layout.tsx

@@ -0,0 +1,26 @@
+import React from "react";
+import { Stack } from "expo-router";
+import { StatusBar } from "expo-status-bar";
+
+export default function RootLayout(): React.ReactElement {
+  return (
+    <>
+      <StatusBar style="light" />
+      <Stack
+        screenOptions={{
+          headerStyle: { backgroundColor: "#1a1f2e" },
+          headerTintColor: "#e1e4ed",
+          headerTitleStyle: { fontWeight: "600" },
+          contentStyle: { backgroundColor: "#0f1419" },
+        }}
+      >
+        <Stack.Screen name="index" options={{ headerShown: false }} />
+        <Stack.Screen name="login" options={{ title: "Sign In" }} />
+        <Stack.Screen name="register" options={{ title: "Create Account" }} />
+        <Stack.Screen name="library" options={{ title: "My Library" }} />
+        <Stack.Screen name="collections" options={{ title: "Collections" }} />
+        <Stack.Screen name="settings" options={{ title: "Settings" }} />
+      </Stack>
+    </>
+  );
+}