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/waybar/shell.nix

@@ -0,0 +1,14 @@
+{ pkgs ? import <nixpkgs> {}
+}:
+
+pkgs.mkShell {
+  packages = with pkgs; [
+    inotify-tools
+    waybar
+    mako
+    swaynotificationcenter
+    libnotify
+    babashka
+    pavucontrol
+  ];
+}