[Tracker] Windows development support — green test suite + tooling

## Problem

Contributors developing on Windows can't run the Astryx test suite and dev tooling cleanly. Failures come from path-separator differences (`/` vs `\`), case-insensitive filesystem behavior (NTFS), and `URL`/`pathname` handling. This raises the barrier to contribution for anyone not on macOS/Linux and lets Windows-only regressions slip in unnoticed.

This is a **tracker** for making Windows a supported development environment this half — the goal is that a contributor on Windows can clone, install, build, and run the full test suite green.

## Scope (on this milestone)

- [ ] #3233 — Test suite fails on Windows due to path-separator and `URL.pathname` issues

## Already fixed (context)

- #3552 — `derivedVarRegistry.test.ts` fails on case-insensitive filesystems (macOS/Windows)
- #3528 — pre-commit hook fails under the pnpm devEngines guard

## Notes

Beyond the known test failures, this should establish a way to catch Windows regressions going forward (e.g. CI coverage on Windows, or documented path/FS conventions) so the environment doesn't silently drift back to broken.

Start with the scoped issue #3233, then reproduce the full test-suite and development-tooling workflow on Windows, including clone, install, and build. Done means the full suite is green on Windows and the project has a stated way to catch future Windows regressions, such as CI coverage or documented path and filesystem conventions.

Written by the indexing model from the issue text.