Document Houdini 22 macOS alignment

[gripeyes]

Compatibility:

build

Issues/Tickets:

#276
#273
#274

Release notes comment:

Documented the experimental Houdini 22 macOS build, integration, and validation workflow.

Comments for the reviewer:

This documentation-only PR records the completed Houdini 22.0.408 validation on Apple Silicon, including:

• The validated Houdini, USD, Python, compiler, and dependency versions.
• The Houdini USD 26.05 imported-target shim.
• The clean dependency and OpenMoonRay build procedure.
• MaterialX shader and Houdini HDA generation.
• The native MoonRay Material Builder, light filters, and tessellation controls.
• The final Hydra/IPR lifecycle fixes and the discarded diagnostic workarounds.
• Houdini launch and environment setup.
• The performed viewport, framebuffer, MaterialX, AOV, and IPR validation.
• Remaining limitations, including disabled Qt applications and Metal rendering.

The existing macOS build guide links to the detailed H22 notes and continues to identify Houdini 20 as the officially supported version.

The historical documentation commits also moved hdMoonray, MCRT, and DCC-plugin submodule pointers. Those pointer changes are deliberately excluded from this focused PR.

Look or scene setup change:

No look or scene setup changes. Documentation only.

Special notes for production:

Houdini 22 support remains experimental. The documented preset paths target Houdini 22.0.408 specifically.

Attention/Reviewers:

AI Assisted Development:

Assisted-by: OpenAI Codex / GPT-5.6

Checklist:

• Documentation has been updated.
• Includes new unit tests.
• Includes new RATS tests.