feat(nixos): add phantom-ship host and streamline server installer ✨

- New host config: phantom-ship.nix (SSH, auto-rebuild, nix-ld, Ethernet)
- Hardware stub: phantom-ship-hardware.nix (replaced by install script)
- Add phantom-ship to flake.nix with home-manager
- Install script now auto-provisions post-install:
  - Clones dotfiles to /etc/dotfiles
  - Installs SSH public key (SSH_PUBKEY_FILE env var)
  - Generates hardware config
  - Supports INSTALLER_HOSTNAME and INSTALLER_DISK env vars
- Fix bootstrap-install.sh default branch to main
- Update CLAUDE.md and server-installer-usb.md

nixos/hosts/phantom-ship-hardware.nix

@@ -0,0 +1,17 @@
+# STUB — replace with output of: nixos-generate-config --show-hardware-config
+# The install script saves the real config here automatically.
+# Filesystems are managed by disko during install; only boot/initrd config here.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+
+  boot.initrd.availableKernelModules = [ "xhci_pci" "ahci" "usb_storage" "sd_mod" ];
+  boot.kernelModules = [ "kvm-intel" ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+  hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
+}