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)

backend/apps/collections/models.py

@@ -0,0 +1,39 @@
+from django.conf import settings
+from django.db import models
+
+
+class Collection(models.Model):
+    """A user-created collection of documents."""
+    name = models.CharField(max_length=300)
+    description = models.TextField(blank=True, default="")
+    cover = models.ImageField(upload_to="collection_covers/", blank=True, null=True)
+    documents = models.ManyToManyField(
+        "documents.Document",
+        related_name="collections",
+        blank=True,
+    )
+    is_public = models.BooleanField(default=False)
+    owner = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="collections",
+    )
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "collections_collection"
+        ordering = ["-updated_at"]
+
+    def __str__(self) -> str:
+        return self.name
+
+    @property
+    def document_count(self) -> int:
+        return self.documents.count()
+
+    @property
+    def cover_url(self) -> str | None:
+        if self.cover:
+            return self.cover.url
+        return None