add image uploads to on-site theme editor and fix scroll on navigation

Phase 4 of unified editing: image upload handling in hook context.
- Configure uploads in Shop.Page mount for logo, header, icon
- Add upload UI components to theme_editor compact_editor
- Pass uploads through page_renderer to theme editor
- Add cancel_upload handler to PageEditorHook

Also fixes scroll position not resetting on patch navigation:
- Push scroll-top event when path changes in handle_params
- JS listener scrolls window to top instantly

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

lib/berrypod_web/page_editor_hook.ex

@@ -740,6 +740,15 @@ defmodule BerrypodWeb.PageEditorHook do
     {:halt, socket}
   end
 
+  defp handle_theme_action(
+         "cancel_upload",
+         %{"ref" => ref, "upload" => upload_name},
+         socket
+       ) do
+    upload_atom = String.to_existing_atom(upload_name)
+    {:halt, Phoenix.LiveView.cancel_upload(socket, upload_atom, ref)}
+  end
+
   # Catch-all for unknown theme actions
   defp handle_theme_action(_action, _params, socket), do: {:halt, socket}