Refactor SSH config to use host-specific keys and disable nix

- Convert SSH config to template with @SSH_KEY@ placeholder
- Add sshKey field to host configurations (mac14, ordio)
- Update home.nix to dynamically substitute SSH keys per host
- Change docker cask to docker-desktop in cask.nix
- Add development packages to ordio host (mkcert, dnsmasq, etc.)
- Disable nix in darwin.nix configuration

hosts/mac14.nix

@@ -2,6 +2,7 @@
   username = "cupcakearmy";
   hostName = "mac14";
   platform = "aarch64-darwin";
+  sshKey = "legba";
 
   extras = {
     casks = [

hosts/ordio.nix

@@ -2,6 +2,7 @@
   username = "nicco";
   hostName = "ordio";
   platform = "aarch64-darwin";
+  sshKey = "ordio";
 
   extras = {
     casks = [