[IMP] website_sale_aplicoop: pay on the checkout page, not a step later

The separate /eskaera/<slug>/payment step is gone. Members review the
summary, choose home delivery and pick a payment method on the checkout,
in one screen; the old URL redirects there so bookmarks and sessions that
were mid-flow do not hit a 404.

The checkout now renders the member's draft sale.order instead of the
localStorage cart. That is what fixes the products appearing "out of
nowhere" between the two pages: the summary was a snapshot of localStorage
taken at page load, and `_autoLoadDraftOnInit` then pulled the draft back
into localStorage without re-rendering. Deleting a product in the shop
removed it from the cart but left the line on the draft, so the autoload
resurrected it, the confirm button sent it back, and it only became
visible one page later. The checkout no longer auto-loads the draft — it
renders it, and what it shows is what the payment form charges.

"Proceed to Checkout" pushes the cart to that draft before navigating.
Saving is idempotent: `_merge_or_replace_draft` reuses the cycle's draft
and, through the new `_draft_matches_lines`, rewrites `order_line` only
when the lines actually differ — replacing them unlinks and recreates
every one of them, which is pure churn when nothing changed.

The home delivery checkbox goes through the new /eskaera/set-home-delivery
so the delivery line moves on the order itself. Writing only to
localStorage would have changed the summary and left the amount alone,
which with online payment on is the amount being charged.

Also fixes the confirmation notice nobody ever saw: saving answered with
the payment step URL and the frontend followed it immediately, destroying
the toast in the same tick. Saving no longer navigates; the caller decides
whether it is staying or moving on.

Along the way: checkout_labels.js and the eskaera_checkout_summary /
eskaera_payment templates are removed, superseded by the server-rendered
summary and checkout, and the stale sessionStorage delivery preference no
longer overrides the checkbox the order just rendered.

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

website_sale_aplicoop/readme/CONFIGURE.rst

@@ -73,9 +73,10 @@ confirms in bulk.
    offer it everywhere, or set it to restrict the provider to one site.
 #. Open the group order form → *Online Payment* tab → tick **Online payment**.
 
-With the flag on, the checkout button becomes "Confirm and pay" and paying is
-the only way to place an order: the member goes through
-``/eskaera/<slug>/payment``, picks a method, and their sale order is confirmed
-as soon as the transaction completes. Members who have not paid by the cutoff
+With the flag on, paying is the only way to place an order: the payment
+methods appear on ``/eskaera/<slug>/checkout``, next to the order summary, and
+the member's sale order is confirmed as soon as the transaction completes.
+There is no separate payment step — the old ``/eskaera/<slug>/payment`` URL
+redirects to the checkout. Members who have not paid by the cutoff
 date still get their draft confirmed by the cron, exactly as they do today —
 the flag decides how orders are placed, not who gets served.

website_sale_aplicoop/readme/USAGE.rst

@@ -50,9 +50,11 @@ Paying an order online
 When the group order has online payment enabled:
 
 #. Build the cart in ``/eskaera/<slug>`` as usual
-#. Go to the checkout, review the summary and choose home delivery if offered
-#. Press **Confirm and pay**: the order is saved and the payment step opens
-#. Pick a payment method and pay; you are sent to the provider and back
+#. Press **Proceed to Checkout**: the cart is saved to your order first, so
+   the checkout shows the very lines and amounts that will be charged
+#. Review the summary, choose home delivery if offered, and pick a payment
+   method — all on the same page
+#. Press **Confirm and pay**; you are sent to the provider and back
 #. The confirmation page shows the outcome and empties the local cart
 
 The order is confirmed the moment the payment goes through, so it can no