Add models and migrations

priv/repo/migrations/20250606131715_create_sessions.exs

@@ -0,0 +1,17 @@
+defmodule Nulla.Repo.Migrations.CreateSessions do
+  use Ecto.Migration
+
+  def change do
+    create table(:sessions) do
+      add :user_id, references(:users, on_delete: :delete_all), null: false
+      add :token, :string, null: false
+      add :user_agent, :string
+      add :ip, :string
+
+      timestamps(type: :utc_datetime)
+    end
+
+    create index(:sessions, [:user_id])
+    create unique_index(:sessions, [:token])
+  end
+end