There is nothing to do at runtime: once the mode is set, ``/shop`` loads its
pages on demand.

How it works
~~~~~~~~~~~~

``/shop`` is rendered by the standard controller, with its pager. When a next
page exists, this module adds a block below the grid carrying the loading mode
and the URL of the current listing (search, category, attributes, tags, price
range and sort order included). The frontend widget then hides the pager and
requests ``/shop/lazy_products?...&page=N``, which answers with the product
cards of that page as an HTML fragment plus whether a further page exists, and
appends them to the grid.

Consequences worth knowing:

* Product links keep the page they belong to (``?page=3``), so coming back from
  a product page lands on the right part of the listing.
* Changing a filter, a category or the sort order is still a normal page load;
  lazy loading restarts from the first page of the new listing.
* Reloading the page starts again from the first page: the appended pages are
  not part of the URL.
* The endpoint answers with the same data ``/shop`` would render for that page,
  under the rights of the visitor making the request.