fix(sat-client): format dates in Mexico City timezone for SAT

formatDateForSat now uses Intl.DateTimeFormat with America/Mexico_City
timezone instead of UTC local time. Fixes 'Fecha final invalida' errors
when server runs in UTC and SAT interprets dates as Mexico local time.

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

@@ -239,10 +239,23 @@ export async function downloadSatPackage(
 }
 
 /**
- * Formatea una fecha para el SAT (YYYY-MM-DD HH:mm:ss)
+ * Formatea una fecha para el SAT (YYYY-MM-DD HH:mm:ss) en hora de México.
+ * El SAT opera en zona horaria America/Mexico_City (UTC-6 estándar).
  */
 function formatDateForSat(date: Date): string {
-  const pad = (n: number) => n.toString().padStart(2, '0');
-  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())} ` +
-    `${pad(date.getHours())}:${pad(date.getMinutes())}:${pad(date.getSeconds())}`;
+  const pad = (n: string) => n.padStart(2, '0');
+  const parts = new Intl.DateTimeFormat('en-US', {
+    timeZone: 'America/Mexico_City',
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+    hour: '2-digit',
+    minute: '2-digit',
+    second: '2-digit',
+    hour12: false,
+  }).formatToParts(date);
+
+  const get = (type: string) => pad(parts.find(p => p.type === type)?.value || '00');
+
+  return `${get('year')}-${get('month')}-${get('day')} ${get('hour')}:${get('minute')}:${get('second')}`;
 }