feat: automatische geplante Backups mit Rotation

Phase 1.3 - Automatische Backups:
- Cron-basierter Scheduler (Standard: täglich 2 Uhr)
- Konfigurierbar über .env (Zeitplan, Verzeichnis, Anzahl)
- Automatische Rotation: behält nur letzte N Backups (Standard: 7)
- UI in Settings → Backup: Status-Anzeige und manueller Trigger
- Tests: 7 erfolgreiche Tests für Scheduler-Funktionalität

Neue Umgebungsvariablen:
- BACKUP_ENABLED (Standard: true)
- BACKUP_SCHEDULE (Standard: 0 2 * * *)
- BACKUP_DIR (Standard: ./backups)
- BACKUP_KEEP (Standard: 7)
- TZ (für Zeitzone)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server/routes/backup.js

@@ -11,6 +11,7 @@ import fs from 'node:fs/promises';
 import { backupToFile, currentVersion, restoreFromFile } from '../db.js';
 import { requireAdmin } from '../auth.js';
 import { createLogger } from '../logger.js';
+import { getStatus as getSchedulerStatus, triggerBackup } from '../services/backup-scheduler.js';
 
 const router = express.Router();
 const log = createLogger('Backup');
@@ -22,10 +23,12 @@ function backupFileName() {
 }
 
 router.get('/status', requireAdmin, (req, res) => {
+  const schedulerStatus = getSchedulerStatus();
   res.json({
     data: {
       schema_version: currentVersion(),
       restore_upload_limit: RESTORE_LIMIT,
+      scheduler: schedulerStatus,
     },
   });
 });
@@ -87,6 +90,16 @@ router.post(
   }
 );
 
+router.post('/trigger', requireAdmin, async (req, res) => {
+  try {
+    const result = await triggerBackup();
+    res.json({ data: result });
+  } catch (err) {
+    log.error('Manual backup trigger failed:', err);
+    res.status(500).json({ error: 'Backup trigger failed.', code: 500 });
+  }
+});
+
 router.use((err, req, res, next) => {
   if (err?.type === 'entity.too.large') {
     return res.status(413).json({ error: `Backup file is too large. Maximum upload size is ${RESTORE_LIMIT}.`, code: 413 });