feat(billing): NexaCloud invoice ledger — ingest invoices to account.move

Odoo becomes the accounting SoR by ingesting NexaCloud's real Stripe
invoices (read-only via the existing DSN) into native account.move
customer invoices: per-service-family income accounts, tax derived to
match the source invoice.tax, Stripe payments reconciled via
account.payment.register (invoice shows paid), idempotent on
x_fc_nexacloud_invoice_id, draft-first with bulk-post + a daily cron
(inactive). Plus a prune helper for the now-obsolete metered shadow data.
73 tests green on odoo-trial. Account codes use dots (Odoo 19 rejects '-').

fusion_centralize_billing/models/__init__.py

@@ -7,3 +7,4 @@ from . import webhook
 from . import reconciliation
 from . import sale_order
 from . import res_partner
+from . import account_move

fusion_centralize_billing/models/account_move.py

@@ -0,0 +1,17 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Nexa Systems Inc.
+# License OPL-1
+from odoo import fields, models
+
+
+class AccountMove(models.Model):
+    _inherit = "account.move"
+
+    x_fc_nexacloud_invoice_id = fields.Char(
+        index=True, copy=False, help="Source NexaCloud invoice id — ledger idempotency key.")
+    x_fc_stripe_invoice_id = fields.Char(index=True, copy=False)
+
+    _fc_nc_invoice_uniq = models.Constraint(
+        "unique(x_fc_nexacloud_invoice_id)",
+        "One Odoo invoice per NexaCloud invoice id.",
+    )