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/__manifest__.py

@@ -49,6 +49,7 @@ reference files from the container before implementing subscription/account inte
         "security/ir.model.access.csv",
         "data/ir_cron.xml",
         "views/import_wizard_views.xml",
+        "views/invoice_ledger_views.xml",
     ],
     "installable": True,
     "application": False,