Use tee so build output appears in both step log and artifact

The build step was using >> to redirect all output to compilation.log,
hiding it from the step log. Since step links now point to the specific
warning line, the output must be visible in the step log. Using tee
sends output to both the file and stdout.

https://claude.ai/code/session_01Eph17CQCfdnKaJhA2nSr9W

Author: claude

.github/workflows/test.yml

@@ -30,7 +30,7 @@ jobs:
       - name: configure
         run: cmake -S. -Bbuild
       - name: build-${{ matrix.os.name }}
-        run: cmake --build build >> compilation.log 2>&1
+        run: cmake --build build 2>&1 | tee compilation.log
       - uses: actions/upload-artifact@v6
         with:
           name: compilation_${{ github.run_id }}_${{ job.check_run_id }}_log