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.
Improves managed_uv.py path resolution for winget/uv installs and updates install.ps1 accordingly. Removes two stale install tests that no longer match the installer's behavior.
Source-level guard (install.ps1 only runs on Windows, so there's no Linux CI
runner to execute it): the astral uv install line must be invoked via the call
operator on a resolved host variable, the bare-`powershell` literal that
produced the field-reported "The term 'powershell' is not recognized" must be
gone, and the resolver must be PATH-independent (Get-Process -Id $PID) and
pwsh-aware.
