feat: Add host sydpc

My, this is a lot TwT.  Much work was batched as part of the transition from
guix-rebound to nixos-testbed/sydpc.

- Discord/Vesktop module & config.
- Syncthing setup.
- Assorted Emacs changes.
- Waybar config.
- Niri config.
- Steam config.
- Some MPD.
- Stylix config.
- Files/Impermanence things.
- Enable Ghostty.
- God knows what else.

modules/home/users/crumb/emacs/modules/syd-lang.el

@@ -2,6 +2,7 @@
              (file-name-concat user-emacs-directory "modules" "lang"))
 
 (require 'syd-lang-agda)
+(require 'syd-lang-kdl)
 (require 'syd-lang-emacs-lisp)
 (require 'syd-lang-clojure)
 (require 'syd-lang-nix)