fix: reduce sync years to 6 (SAT maximum allowed)

SAT only allows downloading CFDIs from the last 6 years.
Reduced from 10 to avoid wasted requests.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/services/sat/sat.service.ts

@@ -13,7 +13,7 @@ import type { Service } from '@nodecfdi/sat-ws-descarga-masiva';
 
 const POLL_INTERVAL_MS = 30000; // 30 segundos
 const MAX_POLL_ATTEMPTS = 60; // 30 minutos máximo
-const YEARS_TO_SYNC = 10;
+const YEARS_TO_SYNC = 6; // SAT solo permite descargar últimos 6 años
 
 interface SyncContext {
   fielData: FielData;