feat(backup): tar.gz format with uploads + manifest, restore guard

- New tar.gz backup format bundling SQLite snapshot + uploads tree + manifest.json (version, app+schema versions, checksums, dbSize)
- BACKUPS_DIR env override; defaults to /app/data/backups in prod, <cwd>/data/backups in dev (matches uploads convention)
- 503 guard in hooks.server.ts while restore is mid-flight (DB file is being swapped); excludes static assets + /api/health; sets Retry-After: 15
- Legacy .db restore still supported (DB-only)
- Restore endpoint adds schema-mismatch detection + force flag; download/schedule endpoints updated
- 256 MiB free-disk safety margin before backup
- tar dep added to package.json; 18 new backupService tests
- i18n labels (en + ru) for new restore/format states

src/lib/utils/validators.ts

@@ -476,7 +476,8 @@ export const auditLogQuerySchema = z.object({
 			AuditAction.EXPORT,
 			AuditAction.BACKUP_CREATED,
 			AuditAction.BACKUP_RESTORED,
-			AuditAction.BACKUP_DELETED
+			AuditAction.BACKUP_DELETED,
+			AuditAction.BACKUP_FAILED
 		])
 		.optional(),
 	entityType: z.string().max(50).optional(),