refactor: move zellij to shared module

nixosModules/zellij/default.nix

@@ -0,0 +1,39 @@
+{
+  lib,
+  pkgs,
+  config,
+}:
+{
+  options.local.zellij = lib.mkEnableOption "zellij" // {
+    default = true;
+  };
+
+  config = lib.mkIf config.local.zellij {
+    local.packages = {
+      inherit (pkgs) zellij;
+    };
+
+    programs.zsh.interactiveShellInit =
+      let
+        monitorScript = pkgs.replaceVarsWith {
+          src = ./monitor.ps;
+          replacements = builtins.mapAttrs (_: lib.getExe) {
+            inherit (pkgs) perl xdotool;
+          };
+          isExecutable = true;
+        };
+      in
+      ''
+        if [[ -z "$ZELLIJ" ]]; then
+          if [[ -n "$SSH_TTY" ]]; then
+            zellij attach -c "SSH@$USER"
+          else
+            MONITOR="$(${monitorScript} || true)"
+            zellij attach -c "''${MONITOR:+"$MONITOR@"}$USER"
+          fi
+          exit
+        fi
+      '';
+
+  };
+}