add reviews schema and context (phase 2)

- Create reviews table with product/order associations
- Add Review schema with create/update/moderation changesets
- Add Reviews context with CRUD, purchase verification, aggregates
- Add get_images/1 to Media, get_variant/1 to Products
- 23 tests covering all context functions

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

priv/repo/migrations/20260401095806_create_reviews.exs

@@ -0,0 +1,27 @@
+defmodule Berrypod.Repo.Migrations.CreateReviews do
+  use Ecto.Migration
+
+  def change do
+    create table(:reviews, 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 :order_id, references(:orders, type: :binary_id, on_delete: :nilify_all)
+      add :email, :string, null: false
+      add :author_name, :string, null: false
+      add :rating, :integer, null: false
+      add :title, :string
+      add :body, :text
+      add :status, :string, null: false, default: "pending"
+      add :image_ids, {:array, :binary_id}, default: []
+
+      timestamps(type: :utc_datetime)
+    end
+
+    create unique_index(:reviews, [:email, :product_id])
+    create index(:reviews, [:product_id, :status])
+    create index(:reviews, [:status])
+  end
+end