feat(wasm-eh): migrate the WASM build to native wasm exceptions (+ 3D viewer default-on)

Replace the legacy Emscripten JS-exceptions model with native wasm-EH (legacy
encoding) across the whole build, keeping Asyncify coroutines working via a
from-source Binaryen --hoist-cpp-catches pre-pass. Net result: native-EH is the
only build mode, the 3D viewer is on by default, and pcbnew shrinks substantially.

Highlights:
- Binaryen submodule everywhere + --hoist-cpp-catches integration in apply-asyncify;
  post-link Asyncify covers every app wasm (not just standalone test wasm).
- Build deps (incl. OpenCASCADE without OCC_CONVERT_SIGNALS) and all KiCad apps
  with -fwasm-exceptions; emscripten_sleep added to the post-link asyncify-imports.
- libcontext fiber entry wired under native exceptions; while-loop main loop +
  currData shim injected into all wx apps.
- Native-EH collab apply fixed: DEBUG-define the embind TU + match all out-of-CMake
  C++ TUs' ABI flags to the core, fixing the vtable-layout skew / mis-dispatch.
- 3D viewer enabled by default (real raytracer linked, not the stub).
- Retire the EH-spike scaffolding; flip the asyncify-races ablation pins to
  shim-redundancy pins (native-EH stays clean with the legacy shims ablated).
- Fix the asyncify-races quiescence check to not require Asyncify.currData==0:
  under the native-EH per-frame-yield top loop the main stack is asyncify-suspended
  every frame, so currData legitimately churns (a freed-but-not-yet-nulled buffer,
  not a leak). Refresh the pcbnew toolbar screenshot baseline for the new kicad.
- CI: drop the obsolete binaryen_version input/env (the build uses the binaryen
  submodule fork's wasm-opt, not a version download); key the wasm-output cache on
  the binaryen submodule SHA instead.

Bumps the wxwidgets + binaryen submodules to their squashed feature commits.

Validated green: all 7 apps native-EH (real 3D in pcbnew); KiCad e2e 63/63
Firefox + Chromium (3D viewer renders); wx 336; coroutine 34/34 both engines;
asyncify 7/7 both engines.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/wasm-exceptions-experiment.md

@@ -5,6 +5,14 @@ codegen bug in emscripten 4.0.2 — see "The blocker" below. The code changes we
 locally and then dropped; the full patch is preserved in the appendix of this doc,
 together with everything needed to resume.
 
+> **Correction 2026-06-22 — see `docs/features/wasm-exceptions/06-spike-plan.md`.** This
+> experiment switched to `-sWASM_LEGACY_EXCEPTIONS=0` (exnref) to dodge the legacy-encoding
+> parse failure — but that is a **dead end**: Binaryen's Asyncify cannot instrument
+> `try_table`/exnref in any released version (incl. v130), so an exnref build would die at
+> the `--asyncify` step even after the `br_table` bug is fixed. **Resume with `=1` (legacy),
+> not `=0`.** The legacy parse failure is almost certainly an em-4.0.2 LLVM-codegen artifact;
+> the fix is the emsdk/LLVM bump, not the encoding switch.
+
 ## Why this matters
 
 After the 3.3x CI win (see `ci-build-slowness-findings.md`), the critical path of the