Add KiCad WASM build infrastructure and dependency scripts

- Add build environment setup (scripts/common/env.sh, versions.sh, functions.sh)
- Add dependency build scripts for Zstd, GLM, FreeType, HarfBuzz, Pixman, Cairo
- Add placeholder scripts for OpenCASCADE, ngspice, protobuf
- Add WASM compatibility layer (wasm/kiplatform/, wasm/libcontext/)
- Add CMake modules for KiCad WASM cross-compilation
- Add PCBnew test infrastructure (tests/kicad/)
- Add build plan documentation

Successfully tested builds: Zstd 1.5.5, GLM 0.9.9.8, FreeType 2.13.2,
HarfBuzz 8.3.0, Pixman 0.42.2, Cairo 1.18.0

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

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

scripts/deps/build-protobuf.sh

@@ -0,0 +1,69 @@
+#!/bin/bash
+# Build Protocol Buffers for WebAssembly
+# Protobuf is used for IPC in KiCad
+
+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"
+
+PROTOBUF_DIR="${DEPS_ROOT}/protobuf-${PROTOBUF_VERSION}"
+PROTOBUF_BUILD="${BUILD_ROOT}/deps/protobuf"
+PROTOBUF_STAMP="${BUILD_ROOT}/stamps/protobuf.stamp"
+
+# Parse arguments
+CLEAN=0
+for arg in "$@"; do
+    case $arg in
+        --clean)
+            CLEAN=1
+            shift
+            ;;
+    esac
+done
+
+if [ $CLEAN -eq 1 ]; then
+    log_info "Cleaning Protobuf build..."
+    rm -rf "${PROTOBUF_BUILD}" "${PROTOBUF_STAMP}"
+fi
+
+# Check if already built
+if check_stamp "${PROTOBUF_STAMP}"; then
+    log_info "Protobuf already built, skipping..."
+    exit 0
+fi
+
+# Download if needed
+if [ ! -d "${PROTOBUF_DIR}" ]; then
+    log_info "Downloading Protobuf ${PROTOBUF_VERSION}..."
+    mkdir -p "${DEPS_ROOT}"
+    cd "${DEPS_ROOT}"
+
+    PROTOBUF_URL="https://github.com/protocolbuffers/protobuf/releases/download/v${PROTOBUF_VERSION}/protobuf-cpp-${PROTOBUF_VERSION}.tar.gz"
+    download_file "${PROTOBUF_URL}" "protobuf-${PROTOBUF_VERSION}.tar.gz"
+    tar -xzf "protobuf-${PROTOBUF_VERSION}.tar.gz"
+    rm "protobuf-${PROTOBUF_VERSION}.tar.gz"
+fi
+
+log_info "Building Protobuf ${PROTOBUF_VERSION} for WASM..."
+
+mkdir -p "${PROTOBUF_BUILD}"
+cd "${PROTOBUF_BUILD}"
+
+emcmake cmake "${PROTOBUF_DIR}" \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DCMAKE_INSTALL_PREFIX="${SYSROOT}" \
+    -DCMAKE_CXX_FLAGS="-pthread" \
+    -Dprotobuf_BUILD_TESTS=OFF \
+    -Dprotobuf_BUILD_EXAMPLES=OFF \
+    -Dprotobuf_BUILD_PROTOC_BINARIES=OFF \
+    -Dprotobuf_BUILD_SHARED_LIBS=OFF \
+    -Dprotobuf_WITH_ZLIB=OFF
+
+emmake make -j${JOBS}
+emmake make install
+
+create_stamp "${PROTOBUF_STAMP}"
+log_info "Protobuf build complete!"