fix(hm/firefox): fix search file conflict

The search file is always replaced by firefox so force replace it as
otherwise home-manager tries to back it up.

modules/hm/gui/default.nix

@@ -64,6 +64,7 @@ in
         enable = true;
         profiles."${config.home.username}" = {
           search = {
+            force = true; # firefox replaces the search settings, force replace them back
             engines =
               let
                 queryParam = name: value: { inherit name value; };