Add setup.sh bootstrap script for fresh machines

Runs the whole README runbook in one go: relocates the repo off the USB
stick, installs CLT + Homebrew, brew bundle, symlinks, copied configs,
fish as default shell, and the .NET SDK, then prints the remaining
manual steps.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MN5eka2MuNJP9uCMdTda75

README.md

@@ -10,7 +10,25 @@ Two kinds of files live here:
 - **Copied** — files that can't be symlinked (`/etc/hosts`, Claude/Serena settings,
   the brewfile). Refresh them from the machine with `./update.fish`.
 
-## Fresh machine setup
+## Fresh machine setup — the fast way
+
+Get this repo onto the machine (USB stick copy or a clone) and run:
+
+```bash
+/bin/bash setup.sh
+```
+
+The script is idempotent and does steps 1–9 below automatically: it copies the
+repo to `~/Repositories/personal/macos-configuration` (so it works straight off
+a USB stick), installs Command Line Tools and Homebrew, runs the brew bundle,
+creates all symlinks, restores the copied configs, sets fish as the default
+shell, and installs the .NET SDK. At the end it prints the manual steps that
+remain (1Password/SSH keys, iTerm2 profile import, `gh auth login` + repo
+cloning, WireGuard, app sign-ins).
+
+The sections below document what the script does, for reference or manual runs.
+
+## Fresh machine setup — step by step
 
 ### 1. Install Command Line Tools and clone this repo