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>

.gitmodules

@@ -3,4 +3,7 @@
 	url = git@github.com:VV-EE/kicad-source-mirror.git
 [submodule "wxwidgets"]
 	path = wxwidgets
-	url = https://github.com/wxWidgets/wxWidgets.git
+	url = git@github.com:VV-EE/wxWidgets.git
+[submodule "wxWidgets-wasm-reference"]
+	path = wxWidgets-wasm-reference
+	url = git@github.com:ahilss/wxWidgets-wasm.git