feat: pl_editor WASM port + browser file dialog fixes

Brings up KiCad's pagelayout_editor (drawing-sheet editor) in the
browser, to roughly the same "boots, canvas visible, partially usable
in-session" level as the existing pcbnew/eeschema/calculator ports.

Build:
- docker/build.sh: add pl_editor to the unified app dispatch (case,
  subdir map, all-loop).
- scripts/kicad/build-kicad-target.sh: add pl_editor to the case;
  upstream target name pl_editor under source subdir pagelayout_editor.
- scripts/kicad/build-pl_editor.sh: 7-line thin wrapper matching the
  pcbnew/eeschema/calculator pattern.
- tests/scripts/setup-kicad-wasm.sh: copy_app pl_editor.

App glue:
- wasm/stubs/nl_pl_editor_plugin_stub.cpp: no-op SpaceMouse plugin so
  pl_editor_frame.cpp's NL_PL_EDITOR_PLUGIN symbols resolve. Mirrors
  nl_pcbnew_plugin_stub.cpp.
- tests/apps/kicad/pl_editor.html: browser shell. preRun creates
  /home/kicad and FS.chdir there so file dialogs land somewhere
  friendly instead of MEMFS root (/dev/, /proc/, etc.).

E2E coverage:
- tests/kicad/pl_editor.spec.ts: 5 tests — smoke (canvas, no abort),
  wizard, File menu has Open/Save As, file-dialog folder-navigation
  regression, canvas + toolbar metrics.
- tests/e2e/filedialog-folder-nav.spec.ts: wxWidgets-level twin of
  the regression test (exercises the underlying widget directly via
  the standalone filedialog_test app).

Submodule bumps:
- kicad → feature/pl-editor (WASM gating in pagelayout_editor's
  CMakeLists + navlib stub).
- wxwidgets → feature/pl-editor (wxGenericFileDialog::OnOk navigates
  into selected directories; wasm/mouse.cpp emits wxEVT_LEFT_DCLICK
  via timestamp-based double-click detection — the latter benefits
  every wxWidgets-WASM app).

See features/pl-editor/ for the design doc + per-repo diff patches.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker/build.sh

@@ -29,7 +29,7 @@ set -e
 
 cd "$(dirname "$0")/.."
 
-VALID_APPS="pcbnew | eeschema | calculator | all"
+VALID_APPS="pcbnew | eeschema | calculator | pl_editor | all"
 
 usage() {
     echo "Usage: ./docker/build.sh <app> [args...]" >&2
@@ -52,7 +52,7 @@ APP_NAME="$1"
 shift
 
 case "$APP_NAME" in
-    pcbnew|eeschema|calculator|all) ;;
+    pcbnew|eeschema|calculator|pl_editor|all) ;;
     *)
         echo "Error: unknown app '$APP_NAME' (expected: ${VALID_APPS})" >&2
         usage
@@ -115,6 +115,7 @@ fi
 kicad_subdir_for() {
     case "$1" in
         calculator) echo "pcb_calculator" ;;
+        pl_editor)  echo "pagelayout_editor" ;;
         *)          echo "$1" ;;
     esac
 }
@@ -158,6 +159,7 @@ if [[ "${APP_NAME}" == "all" ]]; then
     build_app pcbnew
     build_app eeschema
     build_app calculator
+    build_app pl_editor
 else
     build_app "${APP_NAME}"
 fi