[ADD] estate_account: generate invoice on property sale

Introduce a new link module `estate_account` that depends on
`estate` and `account`. This ensures that invoicing is optional
and only available when both modules are installed.

When a property is marked as 'Sold', an invoice is automatically
created in the Invoicing application for the buyer. The invoice
includes two lines:
 - 6% commission fee of the selling price
 - fixed administrative fee of 100.00

This design keeps the estate module independent while allowing
integration with the accounting module for agencies that require
it. By isolating this feature in a link module, we respect Odoo’s
modularity principles and allow users to enable or disable
invoicing without impacting the base real estate workflow.

Author: pusu-odoo

estate_account/__init__.py

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

estate_account/__manifest__.py

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+{
+    "name": "Real Estate Accounting",
+    "descrption": "",
+    "sequence": 2,
+    "category": "Real Estate",
+    "depends": ["estate", "account"],
+    "license": "LGPL-3",
+    "installable": True,
+}

estate_account/models/__init__.py

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+from . import estate_property

estate_account/models/estate_property.py

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+from odoo import models, fields, Command
+
+
+class EstateProperty(models.Model):
+    _inherit = "estate.property"
+
+    def action_set_sold(self):
+        self.env["account.move"].sudo().create(
+            {
+                "partner_id": self.buyer_id.id,
+                "move_type": "out_invoice",
+                "invoice_date": fields.Date.context_today(self),
+                "invoice_line_ids": [
+                    Command.create(
+                        {
+                            "name": self.name,
+                            "quantity": 1,
+                            "price_unit": self.selling_price * 0.06,
+                        }
+                    ),
+                    Command.create(
+                        {
+                            "name": "Administration fees",
+                            "quantity": 1,
+                            "price_unit": 100.00,
+                        }
+                    ),
+                ],
+            }
+        )
+
+        return super().action_set_sold()