feat: configuring shell & add fish shell

modules/home/rsydn/shell/fish.nix

@@ -0,0 +1,17 @@
+{ config, pkgs, lib, ... }: {
+  imports = [ ./oh-my-posh ];
+
+  programs.fish = {
+    enable = true;
+    interactiveShellInit = ''
+      set -g fish_greeting ""
+      set -gx EDITOR nvim
+      set -gx VISUAL nvim
+    '';
+  };
+
+  programs.oh-my-posh.enableFishIntegration = lib.mkDefault true;
+
+  # Ensure fish is available for login shells on Linux hosts.
+  home.packages = lib.mkAfter [ pkgs.fish ];
+}