feat(desktop): toggle the tiling layout on Super+Shift+T

Flip between the dwindle and master layouts with one bind. Neither a
dispatcher nor a keyword toggles the layout on its own, so a small pinned
script reads general:layout and sets the other through hyprctl keyword.

.claude/tasks/0021-desktop-group-and-hyprland-session.md

@@ -60,3 +60,8 @@ Enable the desktop on neogaia.
 - **Dropped from the plan.**
   Mouse drag-to-move and drag-to-resize (`bindm`) were removed: they fall outside the task's enumerated keyboard bindings, and `resizeactive`/`movewindow` already cover floating windows from the keyboard.
   Hardware media/brightness keys (the spec table's `XF86` row) are likewise deferred, since they depend on audio and backlight tooling not yet in scope.
+
+- **Added beyond the plan.**
+  `Super+Shift+T` toggles the tiling strategy between the dwindle and master layouts, added at the operator's request during review.
+  Neither a dispatcher nor a keyword flips the layout on its own, so a small script reads the current layout and sets the other through `hyprctl keyword`.
+  It is not in the spec keybind table.

modules/desktop/hyprland/hyprland.nix

@@ -14,6 +14,16 @@ let
     "$mod, ${toString n}, workspace, ${toString n}"
     "$mod SHIFT, ${toString n}, movetoworkspace, ${toString n}"
   ]) (lib.range 1 9);
+
+  # Flip the tiling strategy between the two built-in layouts, since neither a
+  # dispatcher nor a keyword toggles it on its own.
+  toggleLayout = pkgs.writeShellScript "hypr-toggle-layout" ''
+    if [ "$(hyprctl getoption -j general:layout | ${pkgs.jq}/bin/jq -r .str)" = dwindle ]; then
+      hyprctl keyword general:layout master
+    else
+      hyprctl keyword general:layout dwindle
+    fi
+  '';
 in
 {
   options.modules.desktop.hyprland = {
@@ -122,6 +132,7 @@ in
           "$mod, F, fullscreen,"
           # togglesplit is a dwindle layout message, reached through layoutmsg.
           "$mod, T, layoutmsg, togglesplit"
+          "$mod SHIFT, T, exec, ${toggleLayout}"
           "$mod SHIFT, Q, killactive,"
           "$mod CTRL, Q, forcekillactive,"
         ]