feat(nixos): migrate system configuration

configs/nixos/modules/shell/herdr.nix

@@ -0,0 +1,47 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+# Herdr, a terminal multiplexer for coding agents.
+let
+  cfg = config.modules.shell.herdr;
+  user = config.user.name;
+in
+{
+  options.modules.shell.herdr.enable = lib.mkEnableOption "Herdr, a terminal multiplexer for coding agents";
+
+  config = lib.mkIf cfg.enable {
+    registry.shell-shortcut.${config.networking.hostName}.hs = "herdr --session";
+
+    home-manager.users.${user} = {
+      home.packages = [ pkgs.herdr ];
+
+      xdg.configFile."herdr/config.toml".text = ''
+        [keys]
+        prefix = "ctrl+space"
+        detach = "prefix+d"
+        reload_config = "prefix+r"
+        new_workspace = "prefix+c"
+        new_tab = "prefix+shift+c"
+        rename_workspace = "prefix+comma"
+        rename_tab = "prefix+<"
+        split_vertical = "prefix+backslash"
+        split_horizontal = "prefix+minus"
+        switch_workspace = "prefix+1..9"
+        switch_tab = "prefix+shift+1..9"
+        focus_pane_left = "prefix+h"
+        focus_pane_down = "prefix+j"
+        focus_pane_up = "prefix+k"
+        focus_pane_right = "prefix+l"
+
+        [ui]
+        prompt_new_tab_name = false
+
+        [experimental]
+        kitty_graphics = true
+      '';
+    };
+  };
+}