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/package-lock.json

@@ -15,6 +15,7 @@
         "@nestjs/jwt": "^11.0.2",
         "@nestjs/passport": "^11.0.5",
         "@nestjs/platform-express": "^11.0.1",
+        "@nestjs/schedule": "^12.0.1",
         "@nestjs/swagger": "^11.4.7",
         "@nestjs/throttler": "^6.5.0",
         "@prisma/adapter-pg": "^7.9.1",
@@ -2477,6 +2478,22 @@
         "@nestjs/core": "^11.0.0"
       }
     },
+    "node_modules/@nestjs/schedule": {
+      "version": "12.0.1",
+      "resolved": "https://registry.npmjs.org/@nestjs/schedule/-/schedule-12.0.1.tgz",
+      "integrity": "sha512-v0z/li9L8oxpvuIDAGm5uOLaZ8KzsfZRzgWgppvs5vClneSinZP5IFl3C1F1DCeTCkNLiGN9g/oLUvzg8x++RQ==",
+      "license": "MIT",
+      "dependencies": {
+        "cron": "4.4.0"
+      },
+      "engines": {
+        "node": ">=20.19.0"
+      },
+      "peerDependencies": {
+        "@nestjs/common": "^11.0.0 || ^12.0.0",
+        "@nestjs/core": "^11.0.0 || ^12.0.0"
+      }
+    },
     "node_modules/@nestjs/schematics": {
       "version": "11.1.0",
       "resolved": "https://registry.npmjs.org/@nestjs/schematics/-/schematics-11.1.0.tgz",
@@ -3583,6 +3600,12 @@
       "integrity": "sha512-+K1NIO8I+F9/wNulfVvu23QYd0Pe9/OCqRrim4NoYIf1VoEDL90Ve4ClzpyqBLc7NpGGWRvYNCKZ1BE/Jpf8dQ==",
       "license": "MIT"
     },
+    "node_modules/@types/luxon": {
+      "version": "3.7.5",
+      "resolved": "https://registry.npmjs.org/@types/luxon/-/luxon-3.7.5.tgz",
+      "integrity": "sha512-jJ41Q4z6ZVO260MNDdHfW7+7a5iMiX8Mr6ZJHcmgrvhZha6dz5704o/lF2kKl6URjH6ivEL97w9xS/MgpJEphg==",
+      "license": "MIT"
+    },
     "node_modules/@types/methods": {
       "version": "1.1.4",
       "resolved": "https://registry.npmjs.org/@types/methods/-/methods-1.1.4.tgz",
@@ -5898,6 +5921,23 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/cron": {
+      "version": "4.4.0",
+      "resolved": "https://registry.npmjs.org/cron/-/cron-4.4.0.tgz",
+      "integrity": "sha512-fkdfq+b+AHI4cKdhZlppHveI/mgz2qpiYxcm+t5E5TsxX7QrLS1VE0+7GENEk9z0EeGPcpSciGv6ez24duWhwQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/luxon": "~3.7.0",
+        "luxon": "~3.7.0"
+      },
+      "engines": {
+        "node": ">=18.x"
+      },
+      "funding": {
+        "type": "ko-fi",
+        "url": "https://ko-fi.com/intcreator"
+      }
+    },
     "node_modules/cross-spawn": {
       "version": "7.0.6",
       "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.6.tgz",
@@ -9069,6 +9109,15 @@
         "url": "https://github.com/sponsors/wellwelwel"
       }
     },
+    "node_modules/luxon": {
+      "version": "3.7.2",
+      "resolved": "https://registry.npmjs.org/luxon/-/luxon-3.7.2.tgz",
+      "integrity": "sha512-vtEhXh/gNjI9Yg1u4jX/0YVPMvxzHuGgCm6tC5kZyb08yjGWGnqAjGJvcXbqQR2P3MyMEFnRbpcdFS6PBcLqew==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=12"
+      }
+    },
     "node_modules/magic-string": {
       "version": "0.30.17",
       "resolved": "https://registry.npmjs.org/magic-string/-/magic-string-0.30.17.tgz",