feat(ghostty): enable SSH terminfo propagation and install terminfo on NixOS

Enable ssh-env and ssh-terminfo in Ghostty shell integration for automatic
terminfo handling on remote hosts, and add ghostty.terminfo to NixOS system
packages for coverage when Ghostty SSH wrapper is bypassed.

home/shell/ghostty.nix

@@ -7,6 +7,7 @@
     settings = {
       font-family = "Maple Mono NF CN";
       font-size = 14;
+      shell-integration-features = "cursor,sudo,title,ssh-env,ssh-terminfo";
     };
   };
 }

modules/nixos/base.nix

@@ -6,6 +6,7 @@
   environment.systemPackages = with pkgs; [
     curl
     git
+    ghostty.terminfo
     vim
     wget
   ];