fix production deployment: CSS, images and theme seeding

- Add @source for shop_components/ directory in app-shop.css (Tailwind
  wasn't scanning sub-modules after the refactor, dropping ~73 utilities)
- Remove overly aggressive .dockerignore rules that excluded mockup
  image variants needed by the responsive_image component
- Seed default theme settings on first boot via Release.seed_defaults/0
  in the supervision tree (seeds.exs doesn't run in releases)
- Fix PDP gallery images for mock data by appending -1200.webp to
  bare mockup base paths
- Update fly.toml format from fly launch

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

lib/simpleshop_theme_web/live/shop_live/product_show.ex

@@ -61,6 +61,8 @@ defmodule SimpleshopThemeWeb.ShopLive.ProductShow do
     "/images/#{image_id}/variant/1200.webp"
   end
 
+  # Mock data uses base paths like "/mockups/product-1" — append size + format
+  defp image_src(_, "/mockups/" <> _ = url), do: "#{url}-1200.webp"
   defp image_src(_, url) when is_binary(url), do: url
   defp image_src(_, _), do: nil