add denormalized product fields and use Product structs throughout

Adds cheapest_price, compare_at_price, in_stock, on_sale columns to
products table (recomputed from variants after each sync). Shop
components now work with Product structs directly instead of plain
maps from PreviewData. Renames .name to .title, adds Product display
helpers (primary_image, hover_image, option_types) and ProductImage
helpers (display_url, direct_url, source_width). Adds Products context
query functions for storefront use (list_visible_products,
get_visible_product, list_categories with DB-level sort/filter).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/simpleshop_theme/theme/preview_data_test.exs

@@ -17,10 +17,10 @@ defmodule SimpleshopTheme.Theme.PreviewDataTest do
 
       assert is_map(product)
       assert Map.has_key?(product, :id)
-      assert Map.has_key?(product, :name)
+      assert Map.has_key?(product, :title)
       assert Map.has_key?(product, :description)
-      assert Map.has_key?(product, :price)
-      assert Map.has_key?(product, :image_url)
+      assert Map.has_key?(product, :cheapest_price)
+      assert Map.has_key?(product, :images)
       assert Map.has_key?(product, :category)
       assert Map.has_key?(product, :in_stock)
       assert Map.has_key?(product, :on_sale)
@@ -30,30 +30,26 @@ defmodule SimpleshopTheme.Theme.PreviewDataTest do
       products = PreviewData.products()
 
       for product <- products do
-        assert is_integer(product.price)
-        assert product.price > 0
+        assert is_integer(product.cheapest_price)
+        assert product.cheapest_price > 0
 
         if product.compare_at_price do
           assert is_integer(product.compare_at_price)
-          assert product.compare_at_price > product.price
+          assert product.compare_at_price > product.cheapest_price
         end
       end
     end
 
-    test "products have image URLs" do
+    test "products have images" do
       products = PreviewData.products()
 
       for product <- products do
-        assert is_binary(product.image_url)
-        # Images can be either local paths (starting with /) or full URLs
-        assert String.starts_with?(product.image_url, "/") or
-                 String.starts_with?(product.image_url, "http")
+        assert is_list(product.images)
+        assert length(product.images) >= 1
 
-        if product.hover_image_url do
-          assert is_binary(product.hover_image_url)
-
-          assert String.starts_with?(product.hover_image_url, "/") or
-                   String.starts_with?(product.hover_image_url, "http")
+        for image <- product.images do
+          assert is_integer(image.position)
+          assert is_binary(image.src) or not is_nil(image.image_id)
         end
       end
     end
@@ -109,8 +105,8 @@ defmodule SimpleshopTheme.Theme.PreviewDataTest do
         product = item.product
         assert is_map(product)
         assert Map.has_key?(product, :id)
-        assert Map.has_key?(product, :name)
-        assert Map.has_key?(product, :price)
+        assert Map.has_key?(product, :title)
+        assert Map.has_key?(product, :cheapest_price)
       end
     end
   end