replace nushell with fish

modules/home-manager/features/fish.nix

@@ -0,0 +1,30 @@
+{ config, lib, ... }:
+let
+  feature = "fish";
+in
+{
+  config = lib.mkIf config.${feature}.enable {
+    home.shell.enableFishIntegration = true;
+    programs.fish = {
+      enable = true;
+      interactiveShellInit = ''
+        set fish_greeting
+      '';
+      shellAliases = {
+        cat = "bat";
+        cd = "j";
+        g = "lazygit";
+        l = "eza";
+        la = "eza -a";
+        ls = "eza";
+        ns = "nh os switch";
+        vi = "nvim";
+        vim = "nvim";
+      };
+    };
+  };
+
+  imports = [ ];
+
+  options.${feature}.enable = lib.mkEnableOption "enables ${feature}";
+}