fix(backup): seal backups and require step-up auth to restore

Backups carried every password hash, encrypted MFA secret and webhook
secret in plain JSON, and an import upserted arbitrary rows - including
users - so anyone holding backup:import, or tricking an admin into
importing a file, could overwrite the admin account with a known password.

- Export (download and scheduled) is AES-256-GCM over the gzipped bundle,
  key from BACKUP_ENCRYPTION_KEY or derived from JWT_ACCESS_SECRET via
  HKDF; header is authenticated, decompression is capped. Scheduled files
  are written 0600 in a 0700 directory; run-now returns only the file name.
- Import requires the current password (and TOTP when MFA is on).
- Only a sealed file restores users, roles, grants, webhooks and audit
  entries; an old unsealed file restores business data only and reports
  what it skipped.
- Audit entries are append-only on import.
- Imported documents: entityType checked against the enum, MIME type
  allowlisted and matched against the file signature, path kept under the
  storage root (no more directory traversal via entityType).
- Permission cache is cleared after an import.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

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

@@ -1,10 +1,12 @@
 import { Module } from '@nestjs/common';
+import { ReauthModule } from '../auth/reauth/reauth.module';
 import { BackupController } from './backup.controller';
 import { BackupService } from './backup.service';
 import { BackupSchedulerService } from './backup-scheduler.service';
 import { BackupSettingsService } from './backup-settings.service';
 
 @Module({
+  imports: [ReauthModule],
   controllers: [BackupController],
   providers: [BackupService, BackupSchedulerService, BackupSettingsService],
 })