Add treefmt

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/configs/system/backup/backup.sh

@@ -1,3 +1,5 @@
+# shellcheck shell=bash
+
 if [[ "$EUID" -ne 0 ]]; then
   echo "Please run the script as root."
   exit 1

hosts/common/configs/system/backup/default.nix

@@ -13,8 +13,6 @@
   ];
 
   home-manager.sharedModules = [
-    {
-      programs.zsh.initExtra = builtins.readFile ./backup.completion.zsh;
-    }
+    { programs.zsh.initExtra = builtins.readFile ./backup.completion.zsh; }
   ];
 }