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/common/apply-asyncify.sh

@@ -0,0 +1,60 @@
+#!/bin/bash
+# Apply asyncify transformation to KiCad WASM
+#
+# Usage: ./scripts/common/apply-asyncify.sh <input.wasm> <output.wasm>
+#
+# This script is called by docker/build.sh but can also be run standalone
+# for debugging asyncify issues.
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(cd "${SCRIPT_DIR}/../.." && pwd)"
+
+# Get wasm-opt path
+WASM_OPT=$("${SCRIPT_DIR}/get-wasm-opt.sh")
+
+INPUT_WASM="${1:-output/pcbnew.wasm}"
+OUTPUT_WASM="${2:-${INPUT_WASM}}"
+
+if [ ! -f "${INPUT_WASM}" ]; then
+    echo "ERROR: Input file not found: ${INPUT_WASM}"
+    exit 1
+fi
+
+echo "Applying asyncify transformation..."
+echo "  Input:  ${INPUT_WASM}"
+echo "  Output: ${OUTPUT_WASM}"
+echo "  Tool:   ${WASM_OPT}"
+
+# Asyncify import patterns (functions that trigger async suspension)
+# - env.invoke_* : Exception handling trampolines
+# - env.__asyncjs__* : EM_ASYNC_JS functions (like startModal())
+ASYNCIFY_IMPORTS="env.invoke_*,env.__asyncjs__*"
+
+# Functions to exclude from asyncify instrumentation
+# These are large functions that inflate beyond V8's 7.65MB function limit
+# The names must match exactly as they appear in the WASM (C++ mangled names)
+ASYNCIFY_REMOVE=$(cat << 'REMOVELIST'
+COLOR_SETTINGS::COLOR_SETTINGS(wxString const&, bool)
+BuildBitmapInfo(std::__2::unordered_map<BITMAPS, std::__2::vector<BITMAP_INFO, std::__2::allocator<BITMAP_INFO>>, std::__2::hash<BITMAPS>, std::__2::equal_to<BITMAPS>, std::__2::allocator<std::__2::pair<BITMAPS const, std::__2::vector<BITMAP_INFO, std::__2::allocator<BITMAP_INFO>>>>>&)
+match
+REMOVELIST
+)
+
+# Convert newlines to commas for the removelist
+ASYNCIFY_REMOVE_ARG=$(echo "${ASYNCIFY_REMOVE}" | tr '\n' ',' | sed 's/,$//')
+
+echo ""
+echo "Running wasm-opt --asyncify..."
+echo "This may take several minutes and use significant RAM..."
+
+"${WASM_OPT}" --asyncify \
+    "--pass-arg=asyncify-imports@${ASYNCIFY_IMPORTS}" \
+    "--pass-arg=asyncify-removelist@${ASYNCIFY_REMOVE_ARG}" \
+    --pass-arg=asyncify-propagate-addlist \
+    "${INPUT_WASM}" -o "${OUTPUT_WASM}"
+
+echo ""
+echo "Asyncify complete: ${OUTPUT_WASM}"
+ls -lh "${OUTPUT_WASM}"