Pulls commit 3dab86a95 out of this branch per review — the install.ps1
rewrite (swapping the astral install-script for a direct GitHub-zip
download) is a real Windows-installer behavior change that belongs in
its own installer PR, not riding along in a Desktop E2E PR.
e2e-windows.yml is `if: false` on both jobs and can't run on Linux CI,
so the rewrite lands here with no coverage. The deleted install tests
(test_install_ps1_native_stderr_eap.py,
test_install_ps1_uv_powershell_host.py) are restored — they'll be dropped
alongside the installer change in its own PR.
Original commit 3dab86a95 will be cherry-picked onto a dedicated
installer PR.
0b40ba10cd