optimise product queries: skip image blobs, limit listing preloads, add composite index

The listing preload (images: :image) was loading the full images table row
including the data BLOB column (~3MB per page). Now only loads :id and
:source_width. Listing preloads also limited to first 2 images (primary +
hover) since product cards don't use the rest. Added composite indexes on
(visible, status, inserted_at) and (visible, status, category) to eliminate
the TEMP B-TREE sort SQLite was doing.

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

lib/berrypod_web/live/admin/product_show.ex

@@ -7,7 +7,7 @@ defmodule BerrypodWeb.Admin.ProductShow do
 
   @impl true
   def mount(%{"id" => id}, _session, socket) do
-    case Products.get_product(id, preload: [:provider_connection, images: :image, variants: []]) do
+    case Products.get_product_with_preloads(id) do
       nil ->
         socket =
           socket

lib/berrypod_web/live/admin/products.ex

@@ -64,7 +64,7 @@ defmodule BerrypodWeb.Admin.Products do
   @impl true
   def handle_event("toggle_visibility", %{"id" => id}, socket) do
     product =
-      Products.get_product(id, preload: [:provider_connection, images: :image, variants: []])
+      Products.get_product_with_preloads(id)
 
     case Products.toggle_visibility(product) do
       {:ok, updated} ->