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-Frontend/src/lib/backup/api.ts

@@ -1,5 +1,5 @@
-import { apiFetchBlob, apiFetchFormData, BlobDownload } from "@/lib/auth/api-client";
-import { BackupImportSummary } from "./types";
+import { apiFetch, apiFetchBlob, apiFetchFormData, BlobDownload } from "@/lib/auth/api-client";
+import { BackupImportSummary, BackupScheduleStatus } from "./types";
 
 export function exportBackup(): Promise<BlobDownload> {
   return apiFetchBlob("/backup/export", "apicore-backup.json");
@@ -10,3 +10,13 @@ export function importBackup(file: File): Promise<BackupImportSummary> {
   formData.append("file", file);
   return apiFetchFormData<BackupImportSummary>("/backup/import", formData);
 }
+
+export function getBackupSchedule(): Promise<BackupScheduleStatus> {
+  return apiFetch<BackupScheduleStatus>("/backup/schedule");
+}
+
+export function runBackupNow(): Promise<{ filePath: string }> {
+  return apiFetch<{ filePath: string }>("/backup/schedule/run-now", {
+    method: "POST",
+  });
+}

ApiCore-Frontend/src/lib/backup/types.ts

@@ -1,3 +1,11 @@
 export interface BackupImportSummary {
   imported: Record<string, number>;
 }
+
+export interface BackupScheduleStatus {
+  enabled: boolean;
+  path: string | null;
+  cronSchedule: string | null;
+  retentionCount: number | null;
+  lastRunAt: string | null;
+}