Package the physics engine as an internal @ymir/wasm workspace package
that runs in Node (worker_threads). Parametrize the Emscripten build
(YMIR_WASM_ENVIRONMENT=node, output dir override) so the same C++ core
builds for the server. Expose SimulationEngine interface +
createSimulationEngine() loader mirroring YmirBindings.cpp.
Task: task_01. Tests: 8 passing against the real WASM engine, 100% coverage.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
