Enable notify client and replace swww with awww

- Add `notify.enable = true` to Garand-Desktop, Garand-Laptop, and
  default hosts
- Replace `swww` with `awww` in `essentials.nix`
- Expose `notify-client` in the core packages mapping

modules/core/packages/essentials.nix

@@ -58,7 +58,7 @@
     app2unit
     gpu-screen-recorder
     # hyprland
-    swww
+    awww
     grim
     slurp
     wl-clipboard