Add NixOS server installer USB (disko LUKS + WiFi, hostname prompt)

- disko-server.nix: LUKS + ESP + ext4 root layout for disko-install
- server-install: minimal NixOS config for new servers (hostname/WiFi via --system-config)
- installer-iso: custom minimal ISO with iwlwifi; build with nix build .#installer-iso
- scripts/nixos-server-install.sh: prompt hostname/disk, run disko-install
- docs/server-installer-usb.md: build, write USB, optional live/installed WiFi
- .gitignore: nixos/installer-wifi.nix; AGENTS.md + README.md notes

Made-with: Cursor

nixos/hosts/server-install.nix

@@ -0,0 +1,35 @@
+# Minimal NixOS config for disko-install (new servers).
+# Hostname and WiFi networks are overridden at install time via:
+#   disko-install --system-config '{"networking":{"hostName":"my-server"},...}'
+# No host-specific hardware import; filesystems and LUKS come from disko-server.nix.
+{ config, lib, pkgs, ... }:
+
+{
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+
+  networking.hostName = "nixos";  # Override with --system-config at install
+  networking.wireless.enable = true;
+  # networks."SSID".psk set via --system-config or imperative.conf after boot
+
+  time.timeZone = "Europe/Copenhagen";
+  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+  system.stateVersion = "24.11";
+
+  users.users.danny = {
+    isNormalUser = true;
+    extraGroups = [ "wheel" ];
+    # SSH keys: scp pubkey to server after install, then cat >> ~/.ssh/authorized_keys
+  };
+
+  services.openssh = {
+    enable = true;
+    settings = {
+      PasswordAuthentication = false;
+      KbdInteractiveAuthentication = false;
+    };
+  };
+
+  security.sudo.wheelNeedsPassword = false;
+  environment.systemPackages = [ pkgs.git ];
+}