Add reproducible build system for wxWidgets WASM port

- Add unified patch (wxwidgets-wasm.patch) for build validation
- Add scripts:
  - generate-wxwidgets-patches.sh: Extract patches from wxwidgets state
  - build-wxwidgets-wasm-clean.sh: Build from clean clone + patches
  - build-wxuniversal-wasm.sh: Build wxWidgets for WASM
- Add wxWidgets-wasm-reference submodule (ahilss/wxWidgets-wasm)
- Update .gitignore for wxwidgets-clean/ directory

Base commit: 5ff25322553c1870cf20a2e1ba6f20ed50d9fe9a

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

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

.gitignore

@@ -26,4 +26,7 @@ cmake-build-*/
 .DS_Store
 
 # Emscripten cache
-.emscripten_cache/
+.emscripten_cache/
+
+# Clean clone for reproducible builds (generated by build-wxwidgets-wasm-clean.sh)
+wxwidgets-clean/