7. Как создать общую модель, которая может быть связана с любым типом сущности? (Например, категория или комментарий?).

class Category(models.Model):
    name = models.CharField(max_length=100)
    # ...

    class Meta:
        verbose_name_plural = "Categories"


class Hero(models.Model):
    name = models.CharField(max_length=100)
    category = models.ForeignKey(Category, on_delete=models.CASCADE)
    # ...


class Villain(models.Model):
    name = models.CharField(max_length=100)
    category = models.ForeignKey(Category, on_delete=models.CASCADE)
    # ...

from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
# ...

class FlexCategory(models.Model):
    name = models.SlugField()
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')


class Hero(models.Model):
    name = models.CharField(max_length=100)
    flex_category = GenericRelation(FlexCategory, related_query_name='flex_category')
    # ...


class Villain(models.Model):
    name = models.CharField(max_length=100)
    flex_category = GenericRelation(FlexCategory, related_query_name='flex_category')
    # ...

FlexCategory.objects.create(content_object=hero, name="mythic")

FlexCategory.objects.create(content_object=hero, name="ghost")