Rename azos-core station suite to desktop; move discord out to azos/features

Mirrors the azos-core change: station is renamed desktop (its apps are
generically useful on any machine, work included), discord moves to its
own standalone azos/features/discord (personal-only, so it lives in the
azos project rather than azos-core), and azos-emacs-station becomes
azos-emacs-desktop in lauretta's emacs config to match.

features/discord/default.nix

@@ -0,0 +1,16 @@
+{...}: {
+  config.flake.modules.homeManager.discord = {
+    lib,
+    config,
+    pkgs,
+    ...
+  }: {
+    options.azos.discord.enable = lib.mkOption {
+      default = true;
+      type = lib.types.bool;
+    };
+    config = lib.mkIf config.azos.discord.enable {
+      home.packages = with pkgs; [discord];
+    };
+  };
+}