[ADD] pos_payment_method_cashdro_fix: 17.0 API leftovers in the OCA base module

The 18.0 migration of `pos_payment_method_cashdro` (OCA/pos@6a4c251d) kept
three uses of APIs removed in 18.0. The module has no tests nor tours and needs
a physical drawer to be exercised, so the OCA CI can't catch them:

* `_cashdro_url()` reads `order.selected_paymentline`, so `.payment_method` on
  the resulting `undefined` throws a TypeError on every payment, swallowed into
  a generic "An error occurred while connecting to the cashdro" dialog.
* The `add_paymentline()` patch checks `line.payment_method`, renamed to
  `payment_method_id`, so the line keeps the default due amount instead of
  waiting for the amount the customer inserts.
* `_loader_params_pos_payment_method()` is the 17.0 loading API, replaced by
  `_load_pos_data_fields()`. Dead code, so the CashDro credentials never reach
  the front end.

Patched from the outside, as OCA sources are not to be modified. Written to
stay harmless once fixed upstream: the Python override only adds the missing
fields and the JS patches are idempotent against the fixed code.

`upstream/pos_payment_method_cashdro-18.0-fixes.patch` holds the same fixes as
a ready to send `git format-patch`, verified with `git apply --check`. This
module is temporary and should be removed once that lands in OCA/pos.

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

pos_payment_method_cashdro_fix/models/__init__.py

@@ -0,0 +1 @@
+from . import pos_payment_method

pos_payment_method_cashdro_fix/models/pos_payment_method.py

@@ -0,0 +1,26 @@
+# Copyright 2026 - Today Criptomart
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+from odoo import api
+from odoo import models
+
+CASHDRO_FIELDS = ["cashdro_host", "cashdro_user", "cashdro_password"]
+
+
+class PosPaymentMethod(models.Model):
+    _inherit = "pos.payment.method"
+
+    @api.model
+    def _load_pos_data_fields(self, config_id):
+        """Send the CashDro credentials to the PoS front end.
+
+        `pos_payment_method_cashdro` still declares them through
+        `_loader_params_pos_payment_method`, the 17.0 loading API, which 18.0
+        replaced by this method. That override is dead code, so the front end
+        never receives the host and can't build the CashDro url.
+
+        Only the missing fields are added, so this module stays harmless once
+        the base one is fixed upstream.
+        """
+        fields = super()._load_pos_data_fields(config_id)
+        fields.extend(field for field in CASHDRO_FIELDS if field not in fields)
+        return fields