fix: remove valor field from detallePedido; filter by PREFIJO in transaccion

- json_generator: remove valor entirely from detalle items (not even 0)
- transaccion: after fetching rows, filter by prefix if user typed full
  factura like "LHXC03726" and query returns PREFIJO column

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

app/services/json_generator.py

@@ -153,7 +153,6 @@ def generar_rda_paciente(rows: list, default_profesional: str = "", default_espe
             "codigoBodega": "00",
             "cantidad": 1,
             "tipoUnidad": "D",
-            "valor": 0,
             "descuento": float(row.get("DESCUENTO") or 0),
             "porcentajeIva": 0,
             "impConsumo": 0,