feat: expand backup to all data and add automatic scheduled backups

Backup export/import now covers Role, User, RolePermission,
Notification, AuditLog and Document (with actual file content), not
just business data - matching "wirklich alle Daten". Role/User use
natural keys (role.key, resource+action) so a bundle restores cleanly
into a different database.

Adds BackupSchedulerService (@nestjs/schedule) for cron-based automatic
backups to a local path (BACKUP_STORAGE_PATH), with retention pruning
and a file-mtime guard against duplicate runs across replicas. New
GET /backup/schedule and POST /backup/schedule/run-now endpoints, plus
a status card and manual trigger in the frontend Backup settings page.

ApiCore-Backend/src/backup/backup.controller.ts

@@ -14,6 +14,10 @@ import { RequirePermission } from '../auth/decorators/require-permission.decorat
 import { CurrentUser } from '../auth/decorators/current-user.decorator';
 import type { AuthenticatedUser } from '../auth/types/authenticated-user';
 import { BackupBundle, BackupService } from './backup.service';
+import {
+  BackupScheduleStatus,
+  BackupSchedulerService,
+} from './backup-scheduler.service';
 
 // A full backup bundle can be much larger than the 5mb CSV import cap
 // elsewhere (dozens of tables, potentially years of records, plus embedded
@@ -25,7 +29,22 @@ const MAX_BACKUP_FILE_SIZE_BYTES = 50 * 1024 * 1024;
 @ApiBearerAuth()
 @Controller('backup')
 export class BackupController {
-  constructor(private readonly backupService: BackupService) {}
+  constructor(
+    private readonly backupService: BackupService,
+    private readonly backupSchedulerService: BackupSchedulerService,
+  ) {}
+
+  @RequirePermission('backup:export')
+  @Get('schedule')
+  getSchedule(): Promise<BackupScheduleStatus> {
+    return this.backupSchedulerService.getStatus();
+  }
+
+  @RequirePermission('backup:export')
+  @Post('schedule/run-now')
+  runScheduleNow(): Promise<{ filePath: string }> {
+    return this.backupSchedulerService.runNow();
+  }
 
   @RequirePermission('backup:export')
   @Get('export')