Verify and document the Windows source Quickstart

[reacher-z]

Context

The source-only alpha Quickstart is covered on Linux CI but needs a first-run Windows pass from a clean directory.

Scope

Run the documented clone, locked pnpm install, build, validate, plan, visualize, TypeScript quickstart, and Python quickstart on a supported Windows environment. Update only documentation or narrowly scoped cross-platform command handling discovered by the run.

Acceptance criteria

• Record Windows version, shell, Node version, Python version, pnpm/Corepack version, and uv version.
• Start from a fresh clone with no existing build artifacts.
• Document exact commands and expected output differences.
• Add or update a regression test for any command behavior changed.
• Keep npm and PyPI instructions source-only; packages are not published yet.

Do not include usernames, absolute personal paths, credentials, or private prompts.