Exercise 2: Filtering by Relations — Possible Solution
========================================================

(a) Tags that aren't used on any post

  await prisma.tag.findMany({
    where: { posts: { none: {} } },
  });

  none: {} means "no related post matches an empty condition" — in
  other words, no related posts at all.

(b) Authors with at least one post tagged "prisma"

  await prisma.user.findMany({
    where: {
      posts: { some: { tags: { some: { name: "prisma" } } } },
    },
  });

  Relation filters can be nested: a user with some post, which has
  some tag named "prisma".

(c) Users who have posts, all of them published

  await prisma.user.findMany({
    where: {
      posts: {
        some:  {},                      // has at least one post
        every: { published: true },     // and every post is published
      },
    },
  });

  Without `some: {}`, `every` alone would also return users with no
  posts, because an empty list has no post that breaks the rule.

WHY THIS WORKS AS AN ANSWER
------------------------------
It uses none, nested some, and every — including the empty-list trap
the chapter warns about, which (c) is designed to catch.