feat(billing): subscription creation handler (sale.order is_subscription)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_centralize_billing/models/service.py

@@ -93,3 +93,30 @@ class FusionBillingService(models.Model):
             'included_quota': c.included_quota, 'price_per_unit': c.price_per_unit,
             'unit_batch': c.unit_batch, 'charge_model': c.charge_model,
         } for c in charges]}
+
+    def _api_create_subscription(self, payload):
+        """Create and confirm a subscription sale.order for an external customer.
+
+        The product on each line must have recurring_invoice=True so that
+        Odoo recognises the order as a subscription with has_recurring_line and
+        action_confirm() reaches subscription_state='3_progress'.
+        """
+        self.ensure_one()
+        link = self.env['fusion.billing.account.link'].search([
+            ('service_id', '=', self.id),
+            ('external_id', '=', payload.get('external_customer_id')),
+        ], limit=1)
+        if not link:
+            return {'status': 'error', 'error': 'unknown customer'}
+        order_lines = [(0, 0, {
+            'product_id': line['product_id'],
+            'product_uom_qty': line.get('quantity', 1),
+        }) for line in payload.get('lines', [])]
+        sub = self.env['sale.order'].sudo().create({
+            'partner_id': link.partner_id.id,
+            'plan_id': payload['plan_id'],
+            'order_line': order_lines,
+        })
+        sub.action_confirm()
+        return {'status': 'ok', 'subscription_id': sub.id,
+                'subscription_state': sub.subscription_state}