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>

wasm/cmake/FindGLM.cmake

@@ -0,0 +1,44 @@
+# FindGLM.cmake for WASM cross-compilation
+# This override is needed because CMake's find_file fails during cross-compilation
+# GLM is a header-only library at ${GLM_INCLUDE_DIR}/glm/
+
+# GLM_INCLUDE_DIR should be passed from the build script
+if(NOT GLM_INCLUDE_DIR)
+    message(FATAL_ERROR "GLM_INCLUDE_DIR must be set for WASM builds")
+endif()
+
+# Verify the headers exist
+if(NOT EXISTS "${GLM_INCLUDE_DIR}/glm/glm.hpp")
+    message(FATAL_ERROR "GLM headers not found at ${GLM_INCLUDE_DIR}/glm/glm.hpp")
+endif()
+
+# Extract version from setup.hpp
+file(STRINGS "${GLM_INCLUDE_DIR}/glm/detail/setup.hpp" _glm_version_lines
+    REGEX "^#define[ \t]+GLM_VERSION_(MAJOR|MINOR|PATCH|REVISION)[ \t]+[0-9]+")
+
+foreach(_line ${_glm_version_lines})
+    if(_line MATCHES "GLM_VERSION_MAJOR[ \t]+([0-9]+)")
+        set(_GLM_VERSION_MAJOR ${CMAKE_MATCH_1})
+    elseif(_line MATCHES "GLM_VERSION_MINOR[ \t]+([0-9]+)")
+        set(_GLM_VERSION_MINOR ${CMAKE_MATCH_1})
+    elseif(_line MATCHES "GLM_VERSION_PATCH[ \t]+([0-9]+)")
+        set(_GLM_VERSION_PATCH ${CMAKE_MATCH_1})
+    elseif(_line MATCHES "GLM_VERSION_REVISION[ \t]+([0-9]+)")
+        set(_GLM_VERSION_REVISION ${CMAKE_MATCH_1})
+    endif()
+endforeach()
+
+set(GLM_VERSION "${_GLM_VERSION_MAJOR}.${_GLM_VERSION_MINOR}.${_GLM_VERSION_PATCH}.${_GLM_VERSION_REVISION}")
+
+include(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(GLM
+    REQUIRED_VARS
+        GLM_INCLUDE_DIR
+        GLM_VERSION
+    VERSION_VAR GLM_VERSION)
+
+mark_as_advanced(GLM_INCLUDE_DIR)
+set(GLM_VERSION_MAJOR ${_GLM_VERSION_MAJOR} CACHE INTERNAL "")
+set(GLM_VERSION_MINOR ${_GLM_VERSION_MINOR} CACHE INTERNAL "")
+set(GLM_VERSION_PATCH ${_GLM_VERSION_PATCH} CACHE INTERNAL "")
+set(GLM_VERSION_TWEAK ${_GLM_VERSION_REVISION} CACHE INTERNAL "")