add shipping costs with live exchange rates and country detection

Shipping rates fetched from Printify during product sync, converted to
GBP at sync time using frankfurter.app ECB exchange rates with 5%
buffer. Cached in shipping_rates table per blueprint/provider/country.

Cart page shows shipping estimate with country selector (detected from
Accept-Language header, persisted in cookie). Stripe Checkout includes
shipping_options for UK domestic and international delivery. Order
shipping_cost extracted from Stripe on payment.

ScheduledSyncWorker runs every 6 hours via Oban cron to keep rates
and exchange rates fresh. REST_OF_THE_WORLD fallback covers unlisted
countries. 780 tests, 0 failures.

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

lib/simpleshop_theme/sync/product_sync_worker.ex

@@ -96,6 +96,9 @@ defmodule SimpleshopTheme.Sync.ProductSyncWorker do
           "#{created} created, #{updated} updated, #{unchanged} unchanged, #{errors} errors"
       )
 
+      # Sync shipping rates (non-fatal — logged and skipped on failure)
+      sync_shipping_rates(conn, provider, products)
+
       Products.update_sync_status(conn, "completed", DateTime.utc_now())
       product_count = Products.count_products_for_connection(conn.id)
       broadcast_sync(conn.id, {:sync_status, "completed", product_count})
@@ -200,4 +203,29 @@ defmodule SimpleshopTheme.Sync.ProductSyncWorker do
     # Recompute denormalized fields (cheapest_price, in_stock, on_sale) from variants
     Products.recompute_cached_fields(product)
   end
+
+  defp sync_shipping_rates(conn, provider, products) do
+    if function_exported?(provider, :fetch_shipping_rates, 2) do
+      # Fetch live exchange rates so shipping costs are stored in GBP
+      {:ok, exchange_rates} = SimpleshopTheme.ExchangeRate.fetch_and_cache()
+
+      case provider.fetch_shipping_rates(conn, products) do
+        {:ok, rates} when rates != [] ->
+          SimpleshopTheme.Shipping.upsert_rates(conn.id, rates, exchange_rates)
+
+        {:ok, []} ->
+          Logger.info("No shipping rates returned for #{conn.provider_type}")
+
+        {:error, reason} ->
+          Logger.warning(
+            "Shipping rate sync failed for #{conn.provider_type}: #{inspect(reason)}"
+          )
+      end
+    end
+  rescue
+    e ->
+      Logger.error(
+        "Shipping rate sync crashed for #{conn.provider_type}: #{Exception.message(e)}"
+      )
+  end
 end

lib/simpleshop_theme/sync/scheduled_sync_worker.ex

@@ -0,0 +1,34 @@
+defmodule SimpleshopTheme.Sync.ScheduledSyncWorker do
+  @moduledoc """
+  Oban cron worker for periodic product + shipping rate sync.
+
+  Runs every 6 hours, enqueues a ProductSyncWorker for each enabled
+  provider connection. The :sync queue (concurrency 1) serialises
+  these with any manual syncs triggered from the admin UI.
+  """
+
+  use Oban.Worker, queue: :sync, max_attempts: 1
+
+  alias SimpleshopTheme.Products
+
+  require Logger
+
+  @impl Oban.Worker
+  def perform(%Oban.Job{}) do
+    connections =
+      Products.list_provider_connections()
+      |> Enum.filter(& &1.enabled)
+
+    if Enum.empty?(connections) do
+      Logger.info("Scheduled sync: no enabled provider connections, skipping")
+    else
+      Logger.info("Scheduled sync: enqueuing sync for #{length(connections)} connection(s)")
+
+      Enum.each(connections, fn conn ->
+        Products.enqueue_sync(conn)
+      end)
+    end
+
+    :ok
+  end
+end