Added hetzner server configs

servers/hetzner/modules/services/backup.nix

@@ -0,0 +1,46 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}: let
+  backupScript = pkgs.writeShellScript "weekly-backup" ''
+    BACKUP_DIR="/home/admin/backups"
+    SRC="/home/admin"
+    DATE=$(date +%Y-%m-%dT%H-%M-%S)
+    FILENAME="weekly-backup-$DATE.tar.gz"
+
+    mkdir -p "$BACKUP_DIR"
+    # Backup everything under /home/admin EXCEPT:
+    # - The backups dir itself (infinite loop)
+    # - DMS mail data (GBs of email, backed up separately)
+    # - NixOS-managed service data (at their own paths below)
+    tar czf "$BACKUP_DIR/$FILENAME" \
+      --exclude="$BACKUP_DIR" \
+      --exclude="/home/admin/backups" \
+      --exclude="/home/admin/dms/mail-data" \
+      --exclude="/home/admin/dms/mail-state" \
+      "$SRC"
+
+    # Prune backups older than 14 days
+    find "$BACKUP_DIR" -name "weekly-backup-*" -mtime +14 -delete
+  '';
+in {
+  systemd.services.weekly-backup = {
+    description = "Weekly backup of home directory";
+    path = with pkgs; [coreutils gnutar findutils];
+    serviceConfig = {
+      Type = "oneshot";
+      ExecStart = "${backupScript}";
+      User = "root";
+    };
+  };
+
+  systemd.timers.weekly-backup = {
+    wantedBy = ["timers.target"];
+    timerConfig = {
+      OnCalendar = "Mon *-*-* 03:00:00";
+      Persistent = true;
+    };
+  };
+}