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>

scripts/deps/build-protobuf.sh

@@ -62,8 +62,11 @@ if [ ! -f "${PROTOC_NATIVE}" ]; then
     cd "${PROTOBUF_HOST_BUILD}"
 
     # Build native (not cross-compiled) protoc
+    # Explicitly use system compilers to avoid Emscripten (which is in PATH)
     cmake "${PROTOBUF_DIR}" \
         -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_C_COMPILER=/usr/bin/gcc \
+        -DCMAKE_CXX_COMPILER=/usr/bin/g++ \
         -Dprotobuf_BUILD_TESTS=OFF \
         -Dprotobuf_BUILD_EXAMPLES=OFF \
         -Dprotobuf_BUILD_SHARED_LIBS=OFF \