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>

test/berrypod_web/live/shop/cart_test.exs

@@ -112,7 +112,7 @@ defmodule BerrypodWeb.Shop.CartTest do
     test "page title is Cart", %{conn: conn} do
       {:ok, _view, html} = live(conn, ~p"/cart")
 
-      assert html =~ "<title>Cart</title>"
+      assert html =~ ~r/Cart\s*·\s*Store Name/
     end
   end
 end