fix: ensure CMAKE_PREFIX_PATH is passed to backend builds

- Add CMAKE_ARGS with CMAKE_PREFIX_PATH and OpenMP_ROOT for both HNSW and DiskANN backends
- This ensures CMake can find Homebrew packages on both Intel (/usr/local) and Apple Silicon (/opt/homebrew)
- Fixes the issue where CMake was still looking for hardcoded paths instead of using detected ones

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.github/workflows/build-reusable.yml

@@ -150,6 +150,8 @@ jobs:
             export CC=clang
             export CXX=clang++
             export MACOSX_DEPLOYMENT_TARGET=11.0
+            # Pass CMAKE_PREFIX_PATH to help CMake find Homebrew packages
+            export CMAKE_ARGS="-DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH} -DOpenMP_ROOT=${OpenMP_ROOT}"
             uv build --wheel --python python
           else
             uv build --wheel --python python
@@ -164,6 +166,8 @@ jobs:
             export CXX=clang++
             # DiskANN requires macOS 13.3+ for sgesdd_ LAPACK function
             export MACOSX_DEPLOYMENT_TARGET=13.3
+            # Pass CMAKE_PREFIX_PATH to help CMake find Homebrew packages
+            export CMAKE_ARGS="-DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH} -DOpenMP_ROOT=${OpenMP_ROOT}"
             uv build --wheel --python python
           else
             uv build --wheel --python python