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/documents/models.py

@@ -0,0 +1,48 @@
+from django.conf import settings
+from django.db import models
+
+
+class Document(models.Model):
+    """A digital document (ebook, PDF, etc.) uploaded by a user."""
+
+    class FileType(models.TextChoices):
+        PDF = "pdf", "PDF"
+        EPUB = "epub", "EPUB"
+        MOBI = "mobi", "MOBI"
+        TXT = "txt", "Plain Text"
+        DOCX = "docx", "Word Document"
+
+    title = models.CharField(max_length=500)
+    author = models.CharField(max_length=300, blank=True, null=True)
+    description = models.TextField(blank=True, default="")
+    cover = models.ImageField(upload_to="covers/", blank=True, null=True)
+    file = models.FileField(upload_to="documents/")
+    file_type = models.CharField(max_length=10, choices=FileType.choices)
+    file_size = models.PositiveIntegerField(help_text="File size in bytes")
+    page_count = models.PositiveIntegerField(blank=True, null=True)
+    tags = models.JSONField(default=list, blank=True)
+    is_public = models.BooleanField(default=False)
+    owner = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="documents",
+    )
+    uploaded_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "documents_document"
+        ordering = ["-uploaded_at"]
+        indexes = [
+            models.Index(fields=["owner", "-uploaded_at"]),
+            models.Index(fields=["file_type"]),
+        ]
+
+    def __str__(self) -> str:
+        return self.title
+
+    @property
+    def cover_url(self) -> str | None:
+        if self.cover:
+            return self.cover.url
+        return None