Add standalone test apps and Playwright specs for wxWidgets WASM

- Add 10 standalone test apps for isolated component testing:
  - menu, toolbar, layout, aui, clipboard, filedialog, grid
  - dialog, timer, tree (3 new)
- Add 12 Playwright e2e test specs for automated testing
- Update Makefile with GL/non-GL build configurations
- Update build script to list all standalone tests
- Add WHATWORKS.md documenting KiCad wxWidgets coverage
- Update .gitignore for build artifacts

Test results:
- 79 Playwright tests pass
- wxGrid crashes (memory access out of bounds)
- wxTreeCtrl crashes (similar issue)
- wxDialog/wxMessageBox events fire but no visual popup

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

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

.gitignore

@@ -36,7 +36,12 @@ wxwidgets-clean/
 /tests/node_modules/
 /tests/playwright-report/
 /tests/test-results/
+/test-results/
 /tests/wasm-app/*.js
+/tests/wasm-app/*.html
 /tests/wasm-app/minimal_test.wasm
+/tests/wasm-app/standalone/*/*.js
+/tests/wasm-app/standalone/*/*.html
+/tests/wasm-app/standalone/*/*.wasm
 /temp/
 *.log