[ADD] website_sale_disable_cart: extract cart restriction from website_sale_aplicoop

The "shop as a read-only catalog" behaviour lived inside website_sale_aplicoop,
so every site that wanted the eskaera flow also lost the standard cart. It now
ships as its own installable addon, with the redirect target configurable
instead of hardcoded to /eskaera.

- website_sale_disable_cart: hides the cart UI (12 header styles + the product
  card quick-add) and overrides the standard cart endpoints. Redirect URL is
  configurable in Website settings (default /shop); only site-internal paths are
  accepted, so a misconfigured value cannot turn the shop into an open redirect
  nor loop back into a disabled route.
- Fixes carried over from the original code: /shop/cart/quantity is the Odoo 18
  path (it was /shop/cart_quantity, which never matched), the boxed, sidebar and
  sales two/three/four headers were not covered (the cart link stayed visible on
  them), and the routes now override the standard methods instead of registering
  duplicate ones.
- website_sale_aplicoop 18.0.1.12.0: drops the view file and the four redirect
  routes; installing it no longer touches the standard shop.

Upgrade order matters: update website_sale_aplicoop first, then install
website_sale_disable_cart in a second Odoo run — both use the same XPaths and
obsolete records are only cleaned up at the end of a run.

Tests: 8/8 in website_sale_disable_cart, aplicoop unaffected (its 2 failures
predate this change). Verified live on a DB clone: /shop/cart returns 303 to the
configured URL and no cart markup remains on /shop.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

website_sale_disable_cart/readme/DESCRIPTION.rst

@@ -0,0 +1,25 @@
+This module turns the standard Odoo eCommerce shop into a **read-only product
+catalog**: visitors can browse, search and open product pages, but the standard
+``website_sale`` shopping cart is not reachable any more.
+
+It is meant for sites where the actual ordering happens somewhere else — for
+example the group order flow of ``website_sale_aplicoop`` (``/eskaera``), a
+quotation request form, or an offline/phone process — while the public shop is
+still useful as a catalog.
+
+What it does:
+
+* Hides the cart link and badge from all 12 standard website header styles
+  (default, mobile, hamburger, stretch, vertical, search, boxed, sidebar and
+  sales one to four).
+* Removes the "Add to cart" quick-add area from the product listing cards.
+* Neutralizes the standard cart endpoints:
+
+  * ``/shop/cart`` and ``/shop/cart/update`` redirect to a configurable URL.
+  * ``/shop/cart/update_json`` returns an empty payload (no cart is written).
+  * ``/shop/cart/quantity`` always returns ``0``.
+  * ``/shop/cart/clear`` does nothing.
+
+The redirect target is configurable, so the module stays generic: point it to
+``/shop`` (default) to keep visitors in the catalog, or to whatever route
+implements the real ordering flow of your site.