feat(wasm): occ-split — lazy occ_service worker; kicad_editor drops OCC (−31%)

Move OpenCASCADE out of the merged editor image into occ_service: a separate
emscripten module (-sASYNCIFY=0, MODULARIZE, in-container -Oz finalize, 2N+8
pre-warmed pthread pool) booted lazily in a dedicated Web Worker on the first
STEP export or STEP/IGES model parse. kicad_editor.wasm ~190 MB -> 130 MB;
sessions that never touch OCC never fetch its 57 MB. STEP export works in the
browser for the first time: the unchanged desktop dialog runs EXPORTER_STEP,
whose wasm shadow suspends into globalThis.occService and the export bytes go
straight to a browser download (never entering the editor heap). STEP/IGES 3D
models parse in the worker via the oce shadow (S3D WriteCache/ReadCache wire).

- wasm/occ-service/: service CMake target (hooked from the kicad fork's
  top-level CMakeLists, wasm/editor pattern), embind entry
  (occExport/occLoadModel), wxConfig pre-js.
- wasm/stubs/{exporter_step,oce_plugin}_stub.cpp: EM_ASYNC_JS worker bridges
  (callee-shadowing; no caller #ifdefs).
- web/standalone: provider installed whenever the kicad_editor bundle boots
  (cross-face safe); ONE shared worker-boot source occ-worker.js (vite ?raw;
  the e2e stub reads the same file) — blob worker with locateFile absolutized
  against the glue URL; export download-name guard.
- deps: OCC builds with RapidJSON so its glTF/GLB writer exists — pinned to
  the vcpkg master snapshot 2025-02-26 (24b5e7a8b27f), the same code official
  KiCad consumes via vcpkg.json's opencascade[rapidjson]; rapidjson's latest
  tag (v1.1.0, 2016) is ill-formed under modern clang.
- tests: occ-export dialog e2e (lazy-fetch boundary + STEP download bytes),
  occ-probe incl. a 9-format matrix (step/stpz/brep/xao/ply/stl/glb/u3d/pdf),
  3d-viewer-models hard-asserts the worker parse; occ provider stub installed
  ambiently by the kicad fixtures.

Validated against desktop kicad-cli 10.0.4: geometric exact equality (bbox
delta 0 um, volume delta 0.0000%) for STEP/GLB/STL/BREP/STPZ across three
boards and option sweeps — with desktop OCC 7.9 vs wasm OCC 7.8; PLY/XAO/PDF
structurally equal; U3D same-size (quantizer float LSBs differ). Full kicad
e2e green on Firefox and Chromium; standalone verified end to end (lazy fetch
only on the Export click; export.step 60,628 B ISO-10303-21; loadModel 700 KB
STEP -> 569 KB scenegraph cache).

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

tests/kicad/3d-viewer-models.spec.ts

@@ -183,6 +183,8 @@ test.describe('3D viewer component models', () => {
             fs.readFileSync(fixtureAbs).toString('base64'),
         );
         await installModelProviderStub(page);
+        // (.step models parse in the occ_service worker — the oce3d_Load shadow
+        // suspends on globalThis.occService, installed ambiently by fixtures.)
 
         await loadBoard(page, testLogger);
 
@@ -222,6 +224,16 @@ test.describe('3D viewer component models', () => {
         );
         expect(servedSize, 'served STEP written into the model root').toBeGreaterThan(1000);
 
+        // OCC split: the .step parse runs in the occ_service worker (the oce3d
+        // shadow bridges to it) and must SUCCEED — a boot/bridge failure logs
+        // 'oce Load FAILED' and silently skips the model, which the render
+        // assertions below can miss (hollow green).
+        const oceLoadLines = testLogger.consoleLogs.filter((l) => l.includes('oce Load'));
+        expect(oceLoadLines.some((l) => l.includes('oce Load ok')),
+            'the served STEP must parse in the occ_service worker').toBe(true);
+        expect(oceLoadLines.some((l) => l.includes('oce Load FAILED')),
+            'no oce model parse may fail').toBe(false);
+
         // --- render assertion --------------------------------------------------
         const render = await page.evaluate(() => {
             const list = document.querySelectorAll('canvas[id^="glcanvas-"]');