fix(billing): ledger live-run fixes — UUID cast, UTF-8, reconciling line

Surfaced by the nexamain dry-run against real data:
- reader: cast invoice_items.invoice_id::text (uuid = text[] mismatch).
- readers: set_client_encoding('UTF8') — invoice descriptions contain "×".
- ingest: add a balancing line when invoice.subtotal != sum(items). 9 paid
  base-plan invoices store the charge in subtotal with NO invoice_items, so
  itemized ingestion under-recorded revenue by ~$1,143 (37%); the reconciling
  line makes the Odoo invoice total match what Stripe billed.
74 tests green on odoo-trial.

fusion_centralize_billing/wizards/import_wizard.py

@@ -116,6 +116,7 @@ class FusionBillingImportWizard(models.TransientModel):
             raise UserError("Could not connect to the NexaCloud database: %s" % e)
         try:
             conn.set_session(readonly=True)
+            conn.set_client_encoding('UTF8')
             cur = conn.cursor(cursor_factory=psycopg2.extras.RealDictCursor)
             data = {}
             cur.execute(
@@ -161,6 +162,7 @@ class FusionBillingImportWizard(models.TransientModel):
             raise UserError("Could not connect to the NexaCloud database: %s" % e)
         try:
             conn.set_session(readonly=True)
+            conn.set_client_encoding('UTF8')
             cur = conn.cursor(cursor_factory=psycopg2.extras.RealDictCursor)
             cur.execute(
                 "SELECT subscription_id::text AS sub, "