Remove unused legacy build scripts and directories

Clean up obsolete files that are not part of the current build workflows:

Deleted:
- cmake/ - Old native build CMake modules
- core/ - Old core extraction from Nov 2024
- stubs/ - Old stubs for native build
- scripts/build.sh - Old native build script
- scripts/build-core-wasm.sh - Old core library build
- scripts/build-wxbase-wasm.sh - Old CMake-based wxBase
- scripts/build-kicad-wasm.sh - Old standalone kicad build
- scripts/build-wxwidgets-wasm-clean.sh - Patch testing script
- scripts/generate-wxwidgets-patches.sh - Patch generation
- scripts/prepare.sh - Old patch apply script
- scripts/update-kicad.sh - Old kicad update script
- CMakeLists.txt - Old native build root
- wxWidgets-wasm-reference submodule - Unused reference clone

Both workflows verified working after cleanup:
1. KiCad: docker/build.sh → tests/scripts/setup-kicad-wasm.sh → npm test
2. wxWidgets: scripts/build-wxuniversal-wasm.sh → scripts/build-wasm-test.sh → npm test

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitmodules

@@ -6,6 +6,3 @@
 	path = wxwidgets
 	url = git@github.com:VV-EE/wxWidgets.git
 	branch = wasm-port
-[submodule "wxWidgets-wasm-reference"]
-	path = wxWidgets-wasm-reference
-	url = git@github.com:ahilss/wxWidgets-wasm.git