Integrate BLAS/TLAS acceleration structures and RT shadow compute pass into the deferred rendering demo. Adds GpuContext::new_with_features() for requesting EXPERIMENTAL_RAY_QUERY, Mesh::new_with_usage() for BLAS_INPUT buffer flags, and extends the lighting shadow bind group to 9 entries (shadow map + IBL + SSGI + RT shadow). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>