fix(pos): resolve integration test failures for CFDI + accounting

- Fix sat_accounts.sql: split multi-row INSERT into individual statements
  so parent_id subqueries resolve correctly (was producing all NULLs)
- Add tenant_config table to v1.0 schema (required by CFDI invoicing)
- Seed tenant_config with RFC/regimen during tenant provisioning
- Fix cancel_sale to pass complete sale data for accounting reversal
- Fix CFDI XML builder: use `or` instead of dict.get() defaults to
  handle explicit None values from DB (clave_prod_serv, clave_unidad)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pos/blueprints/invoicing_bp.py

@@ -85,8 +85,8 @@ def _get_sale_with_items(cur, sale_id):
             'tax_rate': float(r[9]) if r[9] else 0.16,
             'tax_amount': float(r[10]) if r[10] else 0,
             'subtotal': float(r[11]) if r[11] else 0,
-            'clave_prod_serv': r[12],
-            'clave_unidad': r[13],
+            'clave_prod_serv': r[12] or '25174800',
+            'clave_unidad': r[13] or 'H87',
         })
 
     return sale