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>

wasm/libcontext/CMakeLists.txt

@@ -0,0 +1,23 @@
+# WASM implementation of libcontext using Emscripten Asyncify
+# Provides fiber/coroutine support for KiCad's router
+
+set(LIBCONTEXT_WASM_SRCS
+    libcontext_wasm.cpp
+)
+
+add_library(libcontext_wasm STATIC ${LIBCONTEXT_WASM_SRCS})
+
+target_include_directories(libcontext_wasm PUBLIC
+    ${CMAKE_CURRENT_SOURCE_DIR}
+)
+
+# Asyncify is required for fiber support
+# These flags must also be set on the final executable
+target_compile_options(libcontext_wasm PRIVATE
+    -pthread
+)
+
+target_link_options(libcontext_wasm INTERFACE
+    -sASYNCIFY=1
+    -sASYNCIFY_STACK_SIZE=65536
+)