Django Dual User System - Admin vs API Users

# Django Dual User System

Two separate user systems: Django admin (auth_user) and API users (custom model).

## Why?
- Admin panel separate from API
- Different authentication (Django sessions vs JWT)
- Same email can be admin AND API user
- Manage API users through admin

## Custom User Model

```python
# core/models.py
import uuid
from django.db import models

class User(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4)
    email = models.EmailField(unique=True)
    password_hash = models.CharField(max_length=255)
    display_name = models.CharField(max_length=255)
    is_active = models.BooleanField(default=True)
    
    # Required for DRF
    @property
    def is_authenticated(self):
        return True
    
    @property
    def is_anonymous(self):
        return False
    
    class Meta:
        db_table = "users"  # NOT auth_user
```

## Register in Admin

```python
# core/admin.py
from django.contrib import admin
from .models import User

@admin.register(User)
class UserAdmin(admin.ModelAdmin):
    list_display = ("email", "display_name", "is_active", "created_at")
    search_fields = ("email", "display_name")
```

## Settings

```python
# settings.py
# DO NOT set AUTH_USER_MODEL
# Django uses built-in User for admin
# Your API uses custom User independently

REST_FRAMEWORK = {
    "DEFAULT_AUTHENTICATION_CLASSES": [
        "api.authentication.JWTAuthentication",
    ],
}
```

## Two Tables

```sql
auth_user:     -- Django admin users
  id (int)
  username (varchar)
  email (varchar)
  
users:         -- API users
  id (uuid)
  email (varchar)
  password_hash (varchar)
```

## Usage

```bash
# Create admin user (auth_user table)
python manage.py createsuperuser

# Create API user (users table)
POST /api/auth/register

# Same email in both = OK!
```

## Advantages
- Isolated systems
- Different auth methods
- Admin manages API users
- No conflicts

## When to Use Single System

If admin and API users are the same:

```python
from django.contrib.auth.models import AbstractBaseUser

class User(AbstractBaseUser, PermissionsMixin):
    # Unified user model
    pass

AUTH_USER_MODEL = "core.User"
```