add site name separator to shop page titles

All shop pages now render as "Page · Store Name" using live_title suffix.
Home stays as "Home · Store Name" for consistency with live navigation.
Updated cart test to use regex for whitespace-tolerant title matching.

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

lib/berrypod_web/components/layouts/shop_root.html.heex

@@ -11,7 +11,9 @@
           "Welcome to #{@theme_settings.site_name}"
       }
     />
-    <.live_title>{assigns[:page_title] || @theme_settings.site_name}</.live_title>
+    <.live_title suffix={" · #{@theme_settings.site_name}"}>
+      {assigns[:page_title]}
+    </.live_title>
     <!-- Preload critical fonts for the current typography preset -->
     <%= for preload <- Berrypod.Theme.Fonts.preload_links(
           @theme_settings.typography,