chore: apply mix format to codebase

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

priv/repo/migrations/20260128235848_create_product_variants.exs

@@ -4,7 +4,10 @@ defmodule SimpleshopTheme.Repo.Migrations.CreateProductVariants do
   def change do
     create table(:product_variants, primary_key: false) do
       add :id, :binary_id, primary_key: true
-      add :product_id, references(:products, type: :binary_id, on_delete: :delete_all), null: false
+
+      add :product_id, references(:products, type: :binary_id, on_delete: :delete_all),
+        null: false
+
       add :provider_variant_id, :string, null: false
       add :title, :string, null: false
       add :sku, :string