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

scripts/bootstrap-install.sh

@@ -1,13 +1,13 @@
 #!/bin/bash
 # Fetch with curl and run to install NixOS (clone + run nixos-server-install.sh).
 # On the live system, run only:
-#   curl -sL https://raw.githubusercontent.com/DannyDannyDanny/dotfiles/server-installer-usb/scripts/bootstrap-install.sh | sudo bash
+#   curl -sL https://raw.githubusercontent.com/DannyDannyDanny/dotfiles/main/scripts/bootstrap-install.sh | sudo bash
 #
 # Optional: REPO_URL=... BRANCH=... (default repo and server-installer-usb)
 set -euo pipefail
 
 REPO_URL="${REPO_URL:-https://github.com/DannyDannyDanny/dotfiles.git}"
-BRANCH="${BRANCH:-server-installer-usb}"
+BRANCH="${BRANCH:-main}"
 DEST="/tmp/dotfiles"
 INSTALL_SCRIPT="$DEST/scripts/nixos-server-install.sh"