feat: Windows setup.ps1 with pre-requisites and delegates to ./setup via Git Bash

[jimmckeeth]

Windows installer PowerShell script that encapsulates ./setup via Git Bash.

On Windows, you can use the PowerShell wrapper instead of ./setup. It auto-installs Node.js, Bun, and Git via winget if they're missing, then delegates to ./setup inside Git Bash. Git Bash has the same home path as Windows (unlike WSL) so the sills install when run outside Git Bash too.

.\setup.ps1 --keep-open --auto
#              ^          ^ Passed to setup
#              | Handled by setup.ps1

The window stays open for 20 seconds after setup completes so you can read the output. Control this with flags:

Flag	Behavior
(default)	Prompts "Autoclose [Y/n]" — auto-closes after 20s
--keep-open	Drops to an interactive bash shell after setup completes
--auto-close	Closes the window immediately on completion

All other flags (--no-browser, --prefix, --no-prefix, --host, etc.) are forwarded to ./setup.