backup: migrate to native services.restic.backups

Replace custom backup-helper flake input with NixOS native
services.restic.backups module for ha1, monitoring01, and nixos-test1.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.lock

@@ -21,27 +21,6 @@
         "url": "https://git.t-juice.club/torjus/alerttonotify"
       }
     },
-    "backup-helper": {
-      "inputs": {
-        "nixpkgs": [
-          "nixpkgs-unstable"
-        ]
-      },
-      "locked": {
-        "lastModified": 1738015166,
-        "narHash": "sha256-573tR4aXNjILKvYnjZUM5DZZME2H6YTHJkUKs3ZehFU=",
-        "ref": "master",
-        "rev": "f9540cc065692c7ca80735e7b08399459e0ea6d6",
-        "revCount": 35,
-        "type": "git",
-        "url": "https://git.t-juice.club/torjus/backup-helper"
-      },
-      "original": {
-        "ref": "master",
-        "type": "git",
-        "url": "https://git.t-juice.club/torjus/backup-helper"
-      }
-    },
     "labmon": {
       "inputs": {
         "nixpkgs": [
@@ -98,7 +77,6 @@
     "root": {
       "inputs": {
         "alerttonotify": "alerttonotify",
-        "backup-helper": "backup-helper",
         "labmon": "labmon",
         "nixpkgs": "nixpkgs",
         "nixpkgs-unstable": "nixpkgs-unstable",