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

backend/config/settings.py

@@ -0,0 +1,42 @@
+import os
+from pathlib import Path
+
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    """Application settings via pydantic-settings. Reads from env vars and .env."""
+
+    # Django
+    DJANGO_SECRET_KEY: str = "django-insecure-change-me-in-production"
+    DJANGO_DEBUG: bool = False
+    DJANGO_ALLOWED_HOSTS: list[str] = ["*"]
+
+    # PostgreSQL
+    DB_NAME: str = "cloud_reader"
+    DB_USER: str = "postgres"
+    DB_PASSWORD: str = "postgres"
+    DB_HOST: str = "localhost"
+    DB_PORT: int = 5432
+
+    # JWT
+    JWT_ACCESS_TOKEN_LIFETIME_MINUTES: int = 60
+    JWT_REFRESH_TOKEN_LIFETIME_DAYS: int = 7
+
+    # CORS
+    CORS_ALLOWED_ORIGINS: list[str] = [
+        "http://localhost:5173",
+        "http://localhost:3000",
+    ]
+
+    @property
+    def DATABASE_URL(self) -> str:
+        return (
+            f"postgresql://{self.DB_USER}:{self.DB_PASSWORD}"
+            f"@{self.DB_HOST}:{self.DB_PORT}/{self.DB_NAME}"
+        )
+
+    model_config = {"env_file": ".env", "env_file_encoding": "utf-8"}
+
+
+settings = Settings()