[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/__manifest__.py

@@ -0,0 +1,23 @@
+# Copyright 2026 - Today Criptomart
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+{
+    "name": "POS CashDro 18.0 Fixes",
+    "version": "18.0.1.0.0",
+    "summary": "Fix the 17.0 API leftovers that break pos_payment_method_cashdro on 18.0",
+    "category": "Point of Sale",
+    "license": "AGPL-3",
+    "author": "Criptomart",
+    "maintainers": ["Criptomart"],
+    "website": "https://git.criptomart.net/criptomart/addons-cm",
+    "depends": [
+        "point_of_sale",
+        "pos_payment_method_cashdro",
+    ],
+    "assets": {
+        "point_of_sale._assets_pos": [
+            "pos_payment_method_cashdro_fix/static/src/js/payment_cashdro_fix.esm.js",
+            "pos_payment_method_cashdro_fix/static/src/js/models_fix.esm.js",
+        ],
+    },
+    "installable": True,
+}