fix: group ventas by NUM_FACTURA, not IDRECEPCION

A single CMXC invoice (e.g. CMXC-307) can have multiple receptions.
Previously each reception was sent as a separate ventas, causing TNS
to accept the first and reject the rest with "ya existe" — leaving
only 1/N of the services registered.

Now agrupar_por_factura groups all receptions sharing the same
NUM_FACTURA into one ventas JSON with all their services in
detallePedido. One factura = one send.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/services/json_generator.py

@@ -125,6 +125,15 @@ def agrupar_por_recepcion(rows: list) -> dict:
     return grupos
 
 
+def agrupar_por_factura(rows: list) -> dict:
+    """Agrupa filas por NUM_FACTURA — para ventas CMXC donde una factura puede tener varias recepciones."""
+    grupos = defaultdict(list)
+    for row in rows:
+        key = str(row.get("NUM_FACTURA") or "")
+        grupos[key].append(dict(row))
+    return grupos
+
+
 def generar_rda_paciente(rows: list, default_profesional: str = "", default_especialidad: str = "",
                          default_remisionante: str = "00", default_prefijo: str = "00",
                          numero_override: str = "", contrato_map: dict = None,