Major config overhaul: use custom modules, setup for multi-host config, and less boilerplate

modules/user/terminal/alacritty.nix

@@ -0,0 +1,19 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.userSettings.alacritty;
+in {
+  options = {
+    userSettings.alacritty = {
+      enable = lib.mkEnableOption "Enable alacritty";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    home.packages = [ pkgs.alacritty ];
+    programs.alacritty.enable = true;
+    programs.alacritty.settings = {
+      window.opacity = lib.mkForce 0.85;
+    };
+  };
+}