fix: backup blockiert HTTP-Response nicht mehr

setImmediate() startet Backup außerhalb des Next.js Request-Kontexts,
ConnectTimeout=15 verhindert hängende SSH-Verbindungen.

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

lib/backup.ts

@@ -1,7 +1,7 @@
 import { spawn } from 'child_process';
 
 export function triggerBackup(): void {
-  runBackup().catch((e) => console.error('[backup] Fehler:', e));
+  setImmediate(() => runBackup().catch((e) => console.error('[backup] Fehler:', e)));
 }
 
 async function runBackup(): Promise<void> {
@@ -32,6 +32,7 @@ async function runBackup(): Promise<void> {
     ...(keyPath ? ['-i', keyPath] : []),
     '-o', 'StrictHostKeyChecking=no',
     '-o', 'BatchMode=yes',
+    '-o', 'ConnectTimeout=15',
   ];
 
   const dumpBin = process.env.BACKUP_DUMP_CMD || 'mariadb-dump';