Add models and migrations

priv/repo/migrations/20250606103707_create_follows.exs

@@ -0,0 +1,15 @@
+defmodule Nulla.Repo.Migrations.CreateFollows do
+  use Ecto.Migration
+
+  def change do
+    create table(:follows) do
+      add :user_id, references(:users, on_delete: :delete_all), null: false
+      add :target_id, references(:users, on_delete: :delete_all), null: false
+
+      timestamps()
+    end
+
+    create unique_index(:follows, [:user_id, :target_id])
+    create index(:follows, [:target_id])
+  end
+end