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/features/async/04-decisions-tests-open-questions.md

@@ -1,5 +1,7 @@
 # 04 — How the fixes relate, the test matrix, open questions
 
+> **STATUS (2026-06-23):** the top-level `set_main_loop(...,1)` `throw "unwind"` treated as current here **is gone** — replaced by the Asyncify **de-park** rAF pump (fatal under native wasm-EH; see [`../wasm-exceptions/09`](../wasm-exceptions/09-event-loop-deparking-plan.md)). The de-park regressed the coroutine suite, and **Design B is now being built to fix it** ([`12`](12-design-b-asyncify-implementation-plan.md) + [`13`](13-design-b-engineering-spec.md)). Read below as the pre-de-park analysis.
+
 > The goal is **one universal mechanism**, not patches scattered around. This file classifies the
 > candidate fixes by *root cause* so it's clear what is part of the one solution, what is
 > subsumed, and what is genuinely separate.