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

modules/user/terminal/default.nix

@@ -0,0 +1,16 @@
+{ config, lib, pkgs, ... }:
+
+{
+  options = {
+    userSettings.terminal = lib.mkOption {
+      default = "alacritty";
+      description = "Default terminal";
+      type = lib.types.enum [ "alacritty" "kitty" ];
+    };
+  };
+
+  config = {
+    userSettings.alacritty.enable = lib.mkDefault (config.userSettings.browser == "brave");
+    userSettings.kitty.enable = lib.mkDefault (config.userSettings.browser == "librewolf");
+  };
+}