package: build the Windows installer with wixl again

[A13xB0]

This branch began as a locale fix. That was wrong, and proving it wrong is what
found the real answer.

WiX cannot build an MSI on Linux

Not "has a bug on Linux". I ran the toolset locally against the .NET runtime,
which turned three CI cycles into three minutes:

• Every Directory/@Name is refused as "not a relative path", whatever the
  name - MeshBench, meshbench, Mesh, mb, A, abc - on a machine with
  a perfectly good en_GB.UTF-8 locale. That is what rules out the locale.
• Remove the Name and it compiles, then dies on
  DllNotFoundException: Unable to load shared library 'msi.dll' - Windows'
  own installer API, which is how WiX writes the database.
• WiX 6.0.2 does exactly the same. WiX 7 refuses to run at all without
  accepting the Open Source Maintenance Fee EULA.

Its own first line of output has been saying this the whole time:
WIX0000: The WiX Toolset only supports Windows. All behavior after this point is undefined.

So the toolset moved for the dialogs (wixl builds none, GNOME/msitools#3) and
could never have worked here. v0.0.5's installer was built by wixl, a native
Linux implementation that needs none of it, and which this job still installs
as part of msitools.

What changed

Restored from v0.0.5: meshbench.wxs, windows-msi.sh, and verify-msi.sh -
that last one had grown assertions for the dialogs and would have refused a
correct wixl package. The WiX setup steps go too; they caused two of tonight's
four faults on their own.

The restored file's line 124 is <Directory Id="INSTALLDIR" Name="MeshBench"/>

• the identical construct WiX rejects and wixl builds without complaint.

Two changes beyond the revert, so the tree does not claim something untrue:

• the changelog entry for the dialogs is gone
• docs/install.md described a folder prompt that will not appear. It now says
  the installer asks nothing, and gives the msiexec INSTALLDIR= and
  MSIINSTALLPERUSER=1 switches - both verified present in the restored .wxs

The locale fix stays. icotool: cannot set locale was a real fault on that
runner, just not the one I was chasing.

What it costs, and what it does not

The install-folder dialog, which has never shipped - 0.0.6 is not out, so
nothing released regresses. 0.0.6's installer is v0.0.5's plus everything else
in the release. Building it on a Windows runner is what the dialogs would cost,
and that is a change to the shape of the pipeline; left for 0.0.7.

Verified

Dispatched build 33850054475,
release: false, no Mac. Windows passed for the first time in this
pipeline:

verify-msi: ...compact.msi is the installer it claims to be
verify-msi: ...bundled.msi is the installer it claims to be
verify-bundle: windows-amd64 bundle carries everything it claims
  qemu-system-xtensa -> qemu/bin/qemu-system-xtensa.exe (63052549 bytes)
  renode -> renode_1.16.1-portable/renode.exe
  libvirtualsx1262.dll (44087 bytes), renode-support -> 12 peripherals

Both MSIs, both zips. Linux green in the same run; macOS and Linux were already
green in the real release build.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Q9HbD44EKWWTRYgxbFGxf6