feat(sway): add the nemo file manager (themed, Mod+e)

Install nemo and bind it to Mod+e (mkForce, overriding the module
default `layout toggle split`). Add a home-manager `gtk` block so GTK
apps match the desktop: the Catppuccin Mocha GTK theme
(catppuccin-gtk, mocha/blue), with Adwaita icons + cursor as before.
Under Sway GTK reads ~/.config/gtk-*/settings.ini directly (no XSettings
daemon), so this themes nemo without extra env.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyrathorpe/home/sway.nix

@@ -131,6 +131,8 @@ in
           # Mod+Space (focus mode_toggle); a plain value would conflict with it
           # at equal priority. Mod+d also still runs the launcher (module default).
           "${modifier}+space" = lib.mkForce "exec ${menu}";
+          # File manager. mkForce overrides the module default (layout toggle split).
+          "${modifier}+e" = lib.mkForce "exec ${pkgs.nemo}/bin/nemo";
           "${modifier}+l" = "exec ${pkgs.swaylock}/bin/swaylock -f";
           "Print" = "exec ${pkgs.grim}/bin/grim ~/screenshot-$(date +%F-%H%M%S).png";
           "XF86AudioRaiseVolume" = "exec ${pkgs.wireplumber}/bin/wpctl set-volume @DEFAULT_AUDIO_SINK@ 5%+";