feat(render-parity): add deterministic frame comparison tool

- Introduced `render-parity` crate for comparing rendered frames against reference images.
- Added command-line options for specifying manifest and output directory.
- Implemented image comparison metrics: mean absolute difference, maximum absolute difference, and changed pixel ratio.
- Created a configuration file `cases.toml` for defining test cases with global defaults and specific parameters.
- Added functionality to capture frames from `render-demo` and save diff images on discrepancies.
- Updated documentation to include usage instructions and CI model for automated testing.

mkdocs.yml

@@ -39,6 +39,7 @@ nav:
       - Network system: specs/network.md
       - NRes / RsLi: specs/nres.md
       - Render pipeline: specs/render.md
+      - Render parity: specs/render-parity.md
       - Runtime pointer: specs/runtime-pipeline.md
       - Sound system: specs/sound.md
       - Terrain + map loading: specs/terrain-map-loading.md