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

systems/portal_1/README.md

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+# portal_1
+
+Minimal NixOS target for a Vultr VM, installed with nixos-anywhere. The Nix
+flake target is `portal_1`; the machine hostname is `portal-1` because DNS
+hostnames cannot contain underscores.
+
+## Before deploying
+
+1. Confirm the VM's system disk is `/dev/vda`. If it is not, update both
+   references in `disk-config.nix`.
+2. Confirm the SSH public key in `default.nix` is the key that should have
+   administrator access.
+3. Boot the VM into a NixOS installer or another nixos-anywhere-compatible
+   Linux rescue environment with root SSH access. Keep this environment
+   running while completing the SOPS bootstrap below.
+
+## Bootstrap SOPS
+
+Use the rescue environment's SSH host key as the permanent portal identity.
+Replace `VM_IP` below:
+
+```console
+ssh root@VM_IP 'cat /etc/ssh/ssh_host_ed25519_key.pub' | \
+  nix shell nixpkgs#ssh-to-age --command ssh-to-age
+```
+
+This prints an `age1...` recipient; it does not copy the private key. Add the
+recipient to `.sops.yaml`:
+
+```yaml
+- &system_portal_1 age1...
+```
+
+Then add `*system_portal_1` to the age recipients for
+`users/secrets.yaml`. Re-encrypt the existing file for the new recipient and
+add the Tailscale key:
+
+```console
+nix shell nixpkgs#sops --command sops updatekeys users/secrets.yaml
+nix shell nixpkgs#sops --command sops users/secrets.yaml
+```
+
+Add the OAuth client secret from the `Auth Keys: Write` credential in the SOPS
+editor and save it:
+
+```yaml
+tailscale_auth_key: tskey-client-...
+```
+
+## Deploy
+
+From the repository root, replace `VM_IP` with the VM's public IP:
+
+```console
+nix run github:nix-community/nixos-anywhere -- \
+  --copy-host-keys --flake .#portal_1 root@VM_IP
+```
+
+This repartitions `/dev/vda`, so anything already on that disk is erased. The
+layout reserves 8 GiB for swap and assigns the remaining space to the root
+filesystem.
+
+`--copy-host-keys` preserves the same private SSH host key at
+`/etc/ssh/ssh_host_ed25519_key` on the installed system. SOPS-Nix converts that
+key to an age identity during activation. After the reboot, connect as
+`richie` and verify that automatic Tailscale enrollment succeeded:
+
+```console
+ssh -p 278 richie@VM_IP
+sudo tailscale status
+```
+
+The installed OpenSSH service listens on port 278. Port 22 is served by
+Endlessh and will not provide an SSH login.
+
+HAProxy uses the same frontend, routing, and rate-limiting configuration as
+Jeeves. Portal manages the ACME certificates for the existing public domains;
+their DNS records must resolve to Portal for HTTP-01 issuance and renewal.
+
+The application backends still use Jeeves' original `127.0.0.1` addresses.
+Replace them with the corresponding Tailscale addresses before directing
+application traffic through Portal. Ports 80 and 443 are allowed through the
+firewall.

systems/portal_1/default.nix

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+{
+  inputs,
+  lib,
+  pkgs,
+  ...
+}:
+{
+  imports = [
+    inputs.disko.nixosModules.disko
+    "${inputs.self}/common/global"
+    "${inputs.self}/users/richie"
+    "${inputs.self}/common/optional/tailscale.nix"
+    ./disk-config.nix
+  ];
+
+  nixpkgs.hostPlatform = "x86_64-linux";
+
+  boot = {
+    # Avoid consuming the VM's limited memory for /tmp.
+    tmp.useTmpfs = false;
+
+    # The Vultr system disk and NIC are exposed as virtio devices.
+    initrd.availableKernelModules = [
+      "virtio_pci"
+      "virtio_blk"
+      "virtio_scsi"
+      "sd_mod"
+    ];
+  };
+
+  networking = {
+    hostName = "portal-1";
+    useDHCP = lib.mkDefault true;
+
+    firewall = {
+      enable = true;
+      allowedTCPPorts = [ 278 ];
+    };
+  };
+
+  services.openssh.ports = [ 278 ];
+
+  environment.systemPackages = with pkgs; [
+    curl
+    htop
+    vim
+  ];
+
+  # The VM uses its regular swap instead of compressed RAM swap.
+  zramSwap.enable = false;
+
+  time.timeZone = "Etc/UTC";
+
+  system.stateVersion = "24.05";
+}

systems/portal_1/disk-config.nix

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+{ ... }:
+{
+  # Vultr's first virtio disk is normally /dev/vda. Change this before
+  # deployment if the selected image exposes its system disk differently.
+  disko.devices.disk.main = {
+    type = "disk";
+    device = "/dev/vda";
+    content = {
+      type = "gpt";
+      partitions = {
+        bios = {
+          size = "1M";
+          type = "EF02";
+        };
+
+        ESP = {
+          size = "512M";
+          type = "EF00";
+          content = {
+            type = "filesystem";
+            format = "vfat";
+            mountpoint = "/boot";
+            mountOptions = [
+              "fmask=0077"
+              "dmask=0077"
+            ];
+          };
+        };
+
+        swap = {
+          size = "8G";
+          content = {
+            type = "swap";
+          };
+        };
+
+        root = {
+          size = "100%";
+          content = {
+            type = "filesystem";
+            format = "ext4";
+            mountpoint = "/";
+          };
+        };
+      };
+    };
+  };
+
+  # Install GRUB for both legacy BIOS and EFI-capable Vultr plans.
+  boot.loader = {
+    grub = {
+      enable = true;
+      devices = [ "/dev/vda" ];
+      efiSupport = true;
+      efiInstallAsRemovable = true;
+    };
+    efi.canTouchEfiVariables = false;
+  };
+}

users/richie/systems/portal-1.nix

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+{
+  imports = [
+    ../home/minimal.nix
+  ];
+}