ci: add GitHub Actions workflow for macOS build

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dev-joss

.github/workflows/build.yml

@@ -0,0 +1,19 @@
+name: Build
+
+on:
+  push:
+    branches: [master, feature/**]
+  pull_request:
+    branches: [master]
+
+jobs:
+  build-macos:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build
+
+      - name: Build
+        run: cmake --build build