Fix Docker macOS timestamp issues and improve build reproducibility

- Add rsync-based source sync for Docker builds to fix macOS VirtioFS
  timestamp inconsistencies that caused autoconf sanity checks to fail
- Add config.sub wrapper (SHELL/CONFIG_SHELL) to support emscripten/wasm32
  targets without modifying submodule files
- Fix protobuf build to use native gcc/g++ for protoc instead of Emscripten
- Add python PATH fix for macOS (Homebrew's python3 symlink) in wxWidgets build

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker/Dockerfile

@@ -18,6 +18,7 @@ RUN apt-get update && apt-get install -y \
     swig \
     unixodbc-dev \
     ccache \
+    rsync \
     && rm -rf /var/lib/apt/lists/*
 
 # Configure ccache for Emscripten