Fix Asyncify and improve build process

Build system improvements:
- Add wasm-opt stub for Docker build to bypass asyncify in container
- Add apply-asyncify.sh script for host-side asyncify transformation
- Update build-pcbnew.sh to install wasm-opt stub and add EXPORTED_RUNTIME_METHODS
- Add --with-zlib=sys to wxWidgets configure for proper zlib linking
- Improve update-baseline-screenshots.sh to only copy new/significantly changed files

wxWidgets submodule update:
- Fix EM_JS to EM_ASYNC_JS for proper Asyncify registration

Test updates:
- Add new baseline screenshots for bitmapbuttons, dnd, gridrenderers, printpreview, specialized tests
- Add kicad-pcbnew initial screenshot
- Fix wxgrid-controls.png and wxgrid-dedicated-page.png (were showing errors)

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

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

scripts/build-wxuniversal-wasm.sh

@@ -98,6 +98,7 @@ emconfigure "$WX_SOURCE/configure" \
     --disable-xlocale \
     --with-cxx=17 \
     --enable-utf8 \
+    --with-zlib=sys \
     ${WX_CONFIGURE_DEBUG}
 
 # Build PCRE first to avoid race condition with parallel builds