[ADD] website_sale_aplicoop: online payment per group order

Members can now pay their eskaera at checkout, through the standard Odoo
payment machinery. Enabled per group order with a new `online_payment`
boolean, off by default: an order without it behaves exactly as before,
members save a draft and the cutoff cron confirms them in bulk.

The flow mirrors website_sale's: the checkout button becomes "Confirm and
pay", saving the cart redirects to a new /eskaera/<slug>/payment step that
renders `payment.form` from `sale`'s `_get_payment_values`, and the standard
/my/orders/<id>/transaction route takes it from there. This addon ships no
provider and configures none; the co-op publishes whichever it wants.

`website_sale`'s `_get_shop_payment_values` is deliberately not reused: it
runs `_get_shop_payment_errors`, which blocks on shippable products without a
delivery method — exactly an eskaera order, collected at the co-op with no
carrier. For the same reason the transaction route stays the portal one,
which does not call `_check_cart_is_ready_to_be_paid()`.

Payment confirms the order, which has three consequences handled here:

* `payment.transaction._check_amount_and_confirm_order` now confirms group
  orders with `from_orderpoint=True`, the way the cutoff cron already does.
  Without it a product with a broken replenishment route raises inside
  `_post_process`, and `/payment/status/poll` rolls back and re-raises: the
  member sees a payment error over a `done` transaction and the retry cron
  fails forever.
* `_confirm_linked_sale_orders` also sweeps the cycle's already confirmed
  orders into the picking batch, scoped by `pickup_date`. Its early return on
  "no drafts" ran before any batching, so a fully prepaid cycle produced no
  batch at all. `_cron_batch_paid_orders_of_closed_cycles` covers the same
  hole for cycles closed by hand.
* A duplicate-order guard answers 409 on save-order, add-to-cart and
  load-draft, and shows a notice on the shop, so a member whose order is
  already placed cannot build and pay for a second one.

The payment policy lives in the model rather than the controller: there are
three sale.order creation paths and two are live, so `_compute_require_payment`
and `_compute_prepayment_percent` are extended instead of patching five vals
dicts. Orders are also created under the group order's company, which is what
filters the payment providers.

Along the way: eskaera drafts were invisible in /my/orders. The portal rule is
`message_partner_ids child_of` and sale.order only subscribes the customer on
send or confirm, never on a draft create, so the `_prepare_orders_domain`
override that includes drafts never had any effect. Fixed with an explicit
`message_subscribe`.

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

website_sale_aplicoop/readme/USAGE.rst

@@ -43,3 +43,21 @@ Order States
 * **Confirmed**: Order open for shopping
 * **Collected**: Orders received from supplier
 * **Completed**: All members have picked up their orders
+
+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
+#. 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
+longer be edited. Coming back to the shop shows a notice with a link to the
+order instead of an empty cart, so nobody pays twice for the same cycle.
+
+If the payment is still being processed when you come back, the page says so
+and the order is confirmed as soon as the provider settles it.