fix(zellij): set default shell

For some reason it fails when trying to start bash.

modules/hm/gui/default.nix

@@ -125,7 +125,17 @@ in
           };
         };
       };
-      zellij.enable = cfg.terminal == "alacritty"; # alacritty has no terminal multiplexer built-in
+      zellij = {
+        enable = cfg.terminal == "alacritty"; # alacritty has no terminal multiplexer built-in
+        # Set default shell
+        settings.default_shell =
+          if config.programs.fish.enable then
+            "fish"
+          else if config.programs.zsh.enable then
+            "zsh"
+          else
+            "bash";
+      };
       # PDF reader
       zathura.enable = true;
       # Auto start sway