Add models and migrations

priv/repo/migrations/20250606103230_create_notifications.exs

@@ -0,0 +1,18 @@
+defmodule Nulla.Repo.Migrations.CreateNotifications do
+  use Ecto.Migration
+
+  def change do
+    create table(:notifications) do
+      add :user_id, references(:users, on_delete: :delete_all), null: false
+      add :actor_id, references(:users, on_delete: :nilify_all)
+      add :type, :string, null: false
+      add :data, :map
+      add :read, :boolean, default: false, null: false
+
+      timestamps()
+    end
+
+    create index(:notifications, [:user_id])
+    create index(:notifications, [:actor_id])
+  end
+end