consolidate shop pages into unified LiveView for editor state persistence

Replace individual shop LiveViews with a single Shop.Page that dispatches
to page modules based on live_action. This enables patch navigation between
pages, preserving socket state (including editor state) across transitions.

Changes:
- Add Shop.Page unified LiveView with handle_params dispatch
- Extract page logic into Shop.Pages.* modules (Home, Product, Collection, etc.)
- Update router to use Shop.Page with live_action for all shop routes
- Change navigate= to patch= in shop component links
- Add maybe_sync_editing_blocks to reload editor state when page changes
- Track editor_page_slug to detect cross-page navigation while editing
- Fix picture element height when hover image disabled
- Extract ThemeEditor components for shared use

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod_web/components/shop_components/cart.ex

@@ -178,7 +178,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
     >
       <%= if @mode != :preview do %>
         <.link
-          navigate={"/products/#{@item.product_id}"}
+          patch={"/products/#{@item.product_id}"}
           class={["cart-item-image", !@item.image && "cart-item-image--empty"]}
           data-size={if @size == :compact, do: "compact"}
           style={if @item.image, do: "background-image: url('#{@item.image}');"}
@@ -197,7 +197,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
         <h3 class="cart-item-name" data-size={if @size == :compact, do: "compact"}>
           <%= if @mode != :preview do %>
             <.link
-              navigate={"/products/#{@item.product_id}"}
+              patch={"/products/#{@item.product_id}"}
               class="cart-item-name-link"
             >
               {@item.name}
@@ -296,7 +296,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
         </button>
       <% else %>
         <.link
-          navigate="/collections/all"
+          patch="/collections/all"
           class="cart-continue-link"
         >
           Continue shopping