fix: backup — error-Events auf spawn abfangen, Tilde in Key-Pfad expandieren

Ohne 'error'-Handler auf den Child-Prozessen führt spawn ENOENT zu
uncaughtException statt zu einem gefangenen Promise-Reject. Außerdem
wird '~' im BACKUP_SSH_KEY_PATH jetzt manuell zu $HOME expandiert,
da spawn keine Shell-Expansion macht.

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

lib/backup.ts

@@ -14,7 +14,10 @@ async function runBackup(): Promise<void> {
     return;
   }
   const [, sshHost, remotePath] = match;
-  const keyPath = process.env.BACKUP_SSH_KEY_PATH || '/app/.ssh/id_rsa';
+  const rawKeyPath = process.env.BACKUP_SSH_KEY_PATH || '/app/.ssh/id_rsa';
+  const keyPath = rawKeyPath.startsWith('~')
+    ? rawKeyPath.replace('~', process.env.HOME || '/root')
+    : rawKeyPath;
 
   const ts = new Date().toISOString().replace('T', '_').replace(/:/g, '-').slice(0, 19);
   const filename = `sternwarte_${ts}.sql.gz`;
@@ -48,6 +51,10 @@ async function runBackup(): Promise<void> {
     dump.stderr.on('data', (d: Buffer) => { dumpErr += d.toString(); });
     ssh.stderr.on('data', (d: Buffer) => { sshErr += d.toString(); });
 
+    dump.on('error', reject);
+    gzip.on('error', reject);
+    ssh.on('error', reject);
+
     dump.on('close', (code) => { if (code !== 0) gzip.stdin.end(); });
     gzip.on('close', () => ssh.stdin.end());
 
@@ -66,6 +73,7 @@ async function runBackup(): Promise<void> {
       ...sshOpts, sshHost,
       `find ${remotePath} -name 'sternwarte_*.sql.gz' -mtime +30 -delete`,
     ]);
+    ssh.on('error', (e) => { console.error('[backup] Cleanup spawn-Fehler:', e.message); resolve(); });
     ssh.on('close', (code) => {
       if (code !== 0) console.error('[backup] Cleanup fehlgeschlagen (exit ' + code + ')');
       resolve();