feat(wasm-dom): dual-mode build scaffold — native DOM port builds, links and boots alongside canvas

Build/test plumbing for the second wxWidgets mode: --dom on
build-wxuniversal-wasm.sh (build-wasm/wxwidgets-dom, no universal,
--disable-tooltips, libwx_wasmu_* stubs) and build-wasm-test.sh
(mirrors sources into tests/apps-dom, PORT=dom). Build script now
reconfigures when Makefile.in or autoconf_inc.m4 regenerate (bakefile
chain). Harness: WX_PORT=dom serves apps-dom, namespaces screenshots
into test-results/dom and logs into logs/wxwidgets/dom; compare/update
screenshot scripts take --port dom with baseline-screenshots-dom.
New port-agnostic boot.spec.ts (green on both ports).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -50,6 +50,14 @@ wxwidgets-clean/
 /tests/apps/standalone/*/*.wasm
 /tests/apps/kicad/*.js
 /tests/apps/kicad/*.wasm
+
+# DOM-port test bundles (mirrored + built by scripts/build-wasm-test.sh --dom)
+/tests/apps-dom/
+
+# Worktree-local canvas reference snapshot for regression gating (see
+# features/wx-dom-port docs); derived from a local run, not a project asset
+/tests/phase0-canvas-reference/
+/tests/phase0-timestamp-noisy.txt
 /tests/apps/kicad/*.tar.gz
 !tests/apps/kicad/pcbnew.html
 /tests/apps/gal-webgl/*.js