Add KiCad PCBnew build script and CMake Find modules

- Add scripts/kicad/build-pcbnew.sh with clean-by-default and --no-clean flag
- Remove old scripts/build-pcbnew-wasm.sh (moved to scripts/kicad/)
- Add Boost build script with Emscripten toolset for Boost.Locale
- Add header download scripts for CURL and libgit2 (stub libraries)
- Add CMake Find modules for cross-compilation compatibility:
  - FindGLM.cmake: Reads version from setup.hpp
  - FindZSTD.cmake: Explicit sysroot paths
  - FindCURL.cmake: Header-only stub
  - FindSPNAV.cmake: Disabled (3D mouse not needed in browser)
  - FindCairo.cmake: Finds our built Cairo
  - FindPixman.cmake: Finds our built Pixman
  - Findlibgit2.cmake: Header-only stub
- Fix OpenCASCADE build: correct extracted dir name, add CMake policy
- Fix Protobuf build: correct GitHub release tag format (v21.12 not v3.21.12)

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

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

scripts/deps/build-boost.sh

@@ -0,0 +1,92 @@
+#!/bin/bash
+# Build Boost for WebAssembly
+# KiCad requires Boost with the locale component
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "${SCRIPT_DIR}/../common/env.sh"
+source "${SCRIPT_DIR}/../common/versions.sh"
+source "${SCRIPT_DIR}/../common/functions.sh"
+
+BOOST_VERSION="${BOOST_VERSION:-1.84.0}"
+BOOST_VERSION_UNDERSCORE="${BOOST_VERSION//./_}"
+BOOST_DIR="${DEPS_ROOT}/boost_${BOOST_VERSION_UNDERSCORE}"
+BOOST_BUILD="${BUILD_ROOT}/deps/boost"
+BOOST_STAMP="${BUILD_ROOT}/stamps/boost.stamp"
+
+# Parse arguments
+CLEAN=0
+for arg in "$@"; do
+    case $arg in
+        --clean)
+            CLEAN=1
+            shift
+            ;;
+    esac
+done
+
+if [ $CLEAN -eq 1 ]; then
+    log_info "Cleaning Boost build..."
+    rm -rf "${BOOST_BUILD}" "${BOOST_STAMP}"
+fi
+
+# Check if already built
+if check_stamp "${BOOST_STAMP}"; then
+    log_info "Boost already built, skipping..."
+    exit 0
+fi
+
+# Download if needed
+if [ ! -d "${BOOST_DIR}" ]; then
+    log_info "Downloading Boost ${BOOST_VERSION}..."
+    mkdir -p "${DEPS_ROOT}"
+    cd "${DEPS_ROOT}"
+
+    # Use SourceForge mirror (most reliable for Boost downloads)
+    BOOST_URL="https://sourceforge.net/projects/boost/files/boost/${BOOST_VERSION}/boost_${BOOST_VERSION_UNDERSCORE}.tar.gz/download"
+    BOOST_ARCHIVE="boost_${BOOST_VERSION_UNDERSCORE}.tar.gz"
+
+    # Download and extract
+    download_file "${BOOST_URL}" "${BOOST_ARCHIVE}"
+    tar -xzf "${BOOST_ARCHIVE}"
+    rm "${BOOST_ARCHIVE}"
+fi
+
+log_info "Building Boost ${BOOST_VERSION} for WASM..."
+
+cd "${BOOST_DIR}"
+
+# Bootstrap b2 if needed
+if [ ! -f "b2" ]; then
+    log_info "Bootstrapping b2..."
+    ./bootstrap.sh --with-toolset=clang
+fi
+
+# Create user-config.jam for Emscripten
+cat > user-config.jam << 'EOF'
+using clang : emscripten
+    : em++
+    : <cxxflags>"-pthread"
+      <linkflags>"-pthread"
+    ;
+EOF
+
+# Build only the locale library (and its dependencies)
+# Most of Boost is header-only, we just need locale built
+log_info "Building Boost.Locale..."
+JOBS=${JOBS:-$(sysctl -n hw.ncpu 2>/dev/null || nproc 2>/dev/null || echo 4)}
+./b2 -j${JOBS} \
+    --user-config=user-config.jam \
+    --prefix="${SYSROOT}" \
+    --with-locale \
+    toolset=clang-emscripten \
+    variant=release \
+    link=static \
+    threading=multi \
+    runtime-link=static \
+    cxxflags="-pthread" \
+    install
+
+create_stamp "${BOOST_STAMP}"
+log_info "Boost build complete!"