refactor: collapse dual-mode plumbing — the DOM port is the only WASM build

The canvas (wxUniversal) mode is gone (wxwidgets submodule); remove every
piece of side-by-side plumbing so there is exactly one build and one test
flow:

- scripts/build-wxuniversal-wasm.sh -> scripts/build-wx-wasm.sh; no
  --dom/--enable-universal; builds into build-wasm/wxwidgets
- build-wasm-test.sh: no DOM_BUILD / apps-dom rsync mirror / PORT=dom;
  apps build straight into tests/apps (Makefile.wasm PORT conditionals
  collapsed; wx.js + wx-dom.js always pre-js)
- docker/build.sh, build-kicad-target.sh, env.sh: WX_PORT / -dom /
  -universal suffixes removed; kicad builds to kicad-<app>, outputs to
  output/; wx.js/wx-dom.js copied from the real source path
  (/workspace/wxwidgets/build/wasm — the old build-wasm path never
  existed and silently failed)
- setup-kicad-wasm.sh: single target dir; the perl wx-dom.js injection is
  gone — the 7 checked-in kicad pages now reference wx-dom.js directly
- playwright configs serve apps/; fixtures drop the test-results/dom and
  logs/wxwidgets/dom namespacing; boot.spec asserts wxDomPort
  unconditionally; pcbnew.spec uses one reference image;
  appearance.spec assertions unconditional
- compare/update-baseline-screenshots.sh: --port removed
- tests/gal-regression/wasm/Makefile: links build-wasm/wxwidgets and
  carries wx-dom.js as a second pre-js — the gal-webgl suite (30 specs)
  now actually builds and runs here (it needed host-side boost+glm via
  scripts/deps; the bundle had been missing, timing the whole spec out)
- tests: clickCanvas() dispatches via page.mouse (DOM widgets
  legitimately cover the canvas; locator actionability refused the
  click); the comprehensive spec drives wxChoice through its native
  <select> (browser-owned popup cannot be coordinate-clicked)
- docs: README/CLAUDE.md/build.md script names and dirs;
  features/wx-dom-port README reframed (DOM is THE port), visual-notes
  bugs 26-28; FindwxWidgets.cmake config label drops 'wasmuniv'
- wxwidgets submodule -> 9dbacc9448 (DOM-only port, fork diff shrunk)

Gate: full wx e2e suite 292 passed / 1 skipped / 0 failed — first run
ever with the gal-webgl specs green (28 scenarios + load + sequential).

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

scripts/common/env.sh

@@ -31,7 +31,7 @@ export STUBS_DIR="$PROJECT_ROOT/stubs"
 export CMAKE_MODULES="$PROJECT_ROOT/cmake"
 
 # wxWidgets build location
-export WX_BUILD="$BUILD_ROOT/wxwidgets-universal"
+export WX_BUILD="$BUILD_ROOT/wxwidgets"
 
 # Emscripten settings
 export EMSDK_QUIET=1