feat: add staged Mac Studio profile

[arbiter-hd]

Summary

• add a staged mac-studio Chezmoi, Homebrew, shell, SSH, and VM profile
• install Ollama without launching it or downloading models
• keep Ubuntu inside the Studio after an explicit, documented cutover
• preserve current thin-Mac, Ubuntu, and Mac-mini routing until arrival
• enforce hardware-arrival and SSH cutover safety gates

Verification

• bash hosts/tests/run.sh
• CHEZMOI_BIN="$HOME/.local/bin/chezmoi" bash chezmoi/tests/production-test.sh
• Bash and Zsh syntax checks
• git diff --check
• Studio Brewfile parse and dry-run
• Standards and spec review passes: no remaining findings

Safety

Pre-arrival only. No bootstrap, package, service, VM, SSH, Apple Account, Tailscale, or Ollama-model changes were applied to a live host.