Scene3D WebAssembly capability probe

This is a retained feasibility test, not a product renderer. It is built only with Emscripten and only when PJ_WASM_SCENE3D_CAPABILITY_PROBE=ON; the option defaults to off and does not enable PJ_WASM_WITH_SCENE3D.

Using the pinned Qt/Emscripten environment:

bash

source /home/davide/emsdk/emsdk_env.sh
cmake -S . -B build-wasm -DPJ_WASM_SCENE3D_CAPABILITY_PROBE=ON
cmake --build build-wasm --target pj_scene3d_wasm_capability_probe -j4
emrun --no-browser --serve-after-exit --port 6931 \
  build-wasm/pj_app/scene3d_capability_probe.html

In another shell, install Chromium and run the probe:

bash

cd tests/wasm
npx playwright install --with-deps chromium
npm run test:scene3d-capability

The server must supply the COOP/COEP headers required by the threaded Qt kit; the test also asserts crossOriginIsolated and SharedArrayBuffer directly. Every run attaches its complete JSON report. The left half of each widget is produced by a vertex-stage texelFetch from a 3D texture, matching the product voxel renderer's capability dependency; the right half retains the fragment-stage sample from an RGBA16F target.

The six .qsb files contain GLSL ES 300 payloads generated with the host Qt 6.11 qsb:

bash

/home/davide/Qt/6.11.0/gcc_64/bin/qsb --glsl "300 es" \
  -o shaders/point.vert.qsb shaders/point.vert

Repeat that command for each shader after editing it. CMake rebakes every pack and compares its hash, so stale committed binaries fail configuration.