Add Emacs desktop provisioning and dev toolchain packages

Install Emacs and copy the desktop .emacs.d config so the editor setup is managed with the rest of desktop dotfiles. Add vterm/build/debug dependencies plus C/C++ and Go tooling needed by the configured workflow.

dotfiles/desktop/.emacs.d/lisp/lang/markdown.el

@@ -0,0 +1,8 @@
+;;; markdown.el -*- lexical-binding: t; -*-
+(use-package markdown-mode
+  :ensure t
+  :mode ("README\\.md\\'" . gfm-mode)
+  :init (setq markdown-command "multimarkdown"))
+
+(provide 'markdown)
+;;; markdown.el ends here