Checkpoint renderer architecture and bootstrap RTXDI

[Hungbocluaqua]

What changed

• Checkpoints the current renderer architecture, diagnostics, pass contracts, editor, streaming, ReSTIR DI/GI, ReGIR, denoising, and temporal-system work.
• Adds the pinned NVIDIA RTXDI-Library submodule and the initial native RTXDI runtime/DXC SPIR-V bootstrap.
• Includes the PathData metadata and half-resolution GI correctness fixes identified during the RTXDI comparison.

Why

This preserves the complete current renderer state before the broader RTXDI-quality and performance implementation proceeds.

Validation

• Release build: passed
• rtvulkan.exe --selftest-renderer-core: passed
• CTest: 7/7 passed