feat(fusion_repairs): sale.order smart buttons - repairs + maintenance

On the original purchase sale.order:
- Repairs button (fa-wrench) lists all repair.order records where
  x_fc_original_sale_order_id = this SO
- Maintenance button (fa-calendar-check-o) lists all
  fusion.repair.maintenance.contract records spawned from this SO
- Both auto-hide when count is zero
- Both gated by fusion_repairs.group_fusion_repairs_user

Follows the count + action_view_* + oe_stat_button / statinfo pattern
from fusion_claims/views/sale_order_views.xml line ~1176.

Co-authored-by: Cursor <cursoragent@cursor.com>

fusion_repairs/models/__init__.py

@@ -15,4 +15,5 @@ from . import res_users
 from . import res_config_settings
 from . import technician_task
 from . import repair_order
+from . import sale_order
 from . import intake_service

fusion_repairs/models/sale_order.py

@@ -0,0 +1,80 @@
+# -*- coding: utf-8 -*-
+# Copyright 2024-2026 Nexa Systems Inc.
+# License OPL-1 (Odoo Proprietary License v1.0)
+
+"""sale.order extensions: smart buttons that link an original purchase SO
+to its downstream repairs, maintenance contracts, and repair invoices.
+
+Mirrors the count + action_view_* pattern from
+fusion_claims/views/sale_order_views.xml line ~1176.
+"""
+
+from odoo import _, api, fields, models
+
+
+class SaleOrder(models.Model):
+    _inherit = 'sale.order'
+
+    x_fc_repair_order_ids = fields.One2many(
+        'repair.order',
+        'x_fc_original_sale_order_id',
+        string='Repairs',
+    )
+    x_fc_repair_order_count = fields.Integer(
+        compute='_compute_x_fc_repair_order_count',
+    )
+
+    x_fc_maintenance_contract_ids = fields.One2many(
+        'fusion.repair.maintenance.contract',
+        'original_sale_order_id',
+        string='Maintenance Contracts',
+    )
+    x_fc_maintenance_contract_count = fields.Integer(
+        compute='_compute_x_fc_maintenance_contract_count',
+    )
+
+    @api.depends('x_fc_repair_order_ids')
+    def _compute_x_fc_repair_order_count(self):
+        for so in self:
+            so.x_fc_repair_order_count = len(so.x_fc_repair_order_ids)
+
+    @api.depends('x_fc_maintenance_contract_ids')
+    def _compute_x_fc_maintenance_contract_count(self):
+        for so in self:
+            so.x_fc_maintenance_contract_count = len(so.x_fc_maintenance_contract_ids)
+
+    def action_view_repair_orders(self):
+        self.ensure_one()
+        if len(self.x_fc_repair_order_ids) == 1:
+            return {
+                'type': 'ir.actions.act_window',
+                'name': self.x_fc_repair_order_ids.name,
+                'res_model': 'repair.order',
+                'view_mode': 'form',
+                'res_id': self.x_fc_repair_order_ids.id,
+            }
+        return {
+            'type': 'ir.actions.act_window',
+            'name': _('Repairs from %(name)s', name=self.name),
+            'res_model': 'repair.order',
+            'view_mode': 'list,form',
+            'domain': [('x_fc_original_sale_order_id', '=', self.id)],
+        }
+
+    def action_view_maintenance_contracts(self):
+        self.ensure_one()
+        if len(self.x_fc_maintenance_contract_ids) == 1:
+            return {
+                'type': 'ir.actions.act_window',
+                'name': self.x_fc_maintenance_contract_ids.name,
+                'res_model': 'fusion.repair.maintenance.contract',
+                'view_mode': 'form',
+                'res_id': self.x_fc_maintenance_contract_ids.id,
+            }
+        return {
+            'type': 'ir.actions.act_window',
+            'name': _('Maintenance Contracts from %(name)s', name=self.name),
+            'res_model': 'fusion.repair.maintenance.contract',
+            'view_mode': 'list,form',
+            'domain': [('original_sale_order_id', '=', self.id)],
+        }