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/bash.nix

@@ -8,6 +8,10 @@ in {
     programs.bash = {
       enable = true;
     };
+
+    home.shellAliases = {
+      nix2json = "nix eval --impure --json --file -";
+    };
   };
 }