feat(portal): add Vultr NixOS host configuration

- use the shared global base and Tailscale module
- configure Portal SSH and VM memory settings
- add Richie's minimal Home Manager profile
- document SOPS and nixos-anywhere deployment

users/richie/systems/portal-1.nix

@@ -0,0 +1,5 @@
+{
+  imports = [
+    ../home/minimal.nix
+  ];
+}