CI: add MSVC activation to the build-wheels Windows job too

The previous MSVC fix landed only in the `test` job, where I assumed
cibuildwheel handled MSVC activation for its Windows wheel builds
automatically. It does not — cibuildwheel's auto-MSVC logic applies to
distutils/setuptools-based projects (where distutils itself knows how
to invoke vcvarsall because Python is built with MSVC), but
meson-python uses meson's own compiler discovery, which picks up the
first C compiler on the runner PATH.

On GitHub Actions' windows-latest, that first compiler is Strawberry
Perl's bundled MinGW-w64 gcc 15.2.0 in C:\Strawberry\c\bin — confirmed
in the wheel build log:

    C compiler for the host machine: C:\Strawberry\c\bin\ccache.EXE cc
    (gcc 15.2.0 "cc (x86_64-posix-seh-rev1, Built by MinGW-Builds
    project) 15.2.0")

The resulting .pyd files link against libgomp-1.dll / libgcc_s_seh-1.dll
which are not on the wheel-test environment's DLL search path, so
cibuildwheel's own test phase fails with the same ImportError we
already diagnosed for the test job.

Fix: add `ilammy/msvc-dev-cmd@v1` step before the cibuildwheel step in
the build-wheels job, conditional on runner.os == 'Windows'. The
existing step in the test job is unchanged.

Also update ~/.claude/CI-SETUP-NOTES.md and ~/.claude/CLAUDE.md to
state that the MSVC activation step needs to land in BOTH jobs, not
just the test job (my earlier writeup incorrectly claimed cibuildwheel
handled the build-wheels side automatically).

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: Technologicat

.github/workflows/ci.yml

@@ -94,9 +94,20 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
+      # Same MSVC activation as in the test job, and for the same reason:
+      # cibuildwheel does NOT automatically activate MSVC for meson-python
+      # builds on Windows (unlike distutils/setuptools-based projects where
+      # distutils auto-detects MSVC via the python-being-built-with logic).
+      # Without this step, meson picks up Strawberry Perl's bundled
+      # MinGW-w64 gcc from the runner PATH and the resulting .pyd files
+      # link against libgomp-1.dll / libgcc_s_seh-1.dll, which are not
+      # present in the wheel test environment.
+      - uses: ilammy/msvc-dev-cmd@v1
+        if: runner.os == 'Windows'
+
       # cibuildwheel config lives in pyproject.toml ([tool.cibuildwheel]) —
       # build list, skip list, test-requires, test-command, and the macOS
-      # before-all that installs libomp.
+      # before-all that installs conda-forge llvm-openmp via micromamba.
       - uses: pypa/[email protected]
 
       - uses: actions/upload-artifact@v7