Agent-friendly conventions for openusd-cheatsheet.md

[asluk]

Initial pass at agent-friendly conventions. Adds metadata, source/scope tags, recast Agents section, plus folded-in framing/factual fixes. Follow-up commits welcome on the items in Out of scope below.

Why

#71 added docs/openusd-cheatsheet.md as a human-readable single-page entrypoint. Real-world consumption is mixed — humans skim it, agents (LLMs, MCP servers, RAG pipelines) ingest it. Agents need signals humans infer from context: vendor scope (OpenUSD vs NVIDIA), renderer scope (Kit vs OVRTX), freshness, validation-layer disambiguation, decision rubrics over flat lists.

This PR makes those signals explicit and machine-readable without bloating the page for humans.

What's in this PR

Front-matter metadata (HTML comment)

Invisible in rendered view; parseable by anything reading the markdown source.

<!--
agent-readable metadata:
  last_verified: 2026-04-29
  openusd_version_target: "25.05+"
  maintained_by: NVIDIA-Omniverse
  audience: [humans, agents]
  tag_vocabulary: ...
-->

Source/scope tags on every link

Tag vocabulary: [OpenUSD], [NVIDIA], [Kit], [OVRTX], [Isaac], [Community]. Multiple tags allowed.

Example:

- [Maximizing USD Performance](https://openusd.org/release/maxperf.html) `[OpenUSD]`
- [Kit Scene Optimizer](https://docs.omniverse.nvidia.com/extensions/latest/ext_scene-optimizer.html) `[NVIDIA, Kit]`

Quick visual scan for humans; structural metadata for agents; vendor-neutrality becomes grep-able.

Recast ## Agents section — instructions for agents, not about them

Drops the "Current models (GPT 5, Opus 4)" snapshot (which dates fast). Replaces with:

• Routing guidance (prefer [OpenUSD] first, then [NVIDIA])
• Renderer scope reminder (distinguish [OVRTX] from [Kit])
• Layer disambiguation pointer (match user intent to validation layer)
• Freshness verification (last_verified in metadata)
• A list of NVIDIA OpenUSD-related MCP servers (kit-dev, usd-code, isaac-sim, omni-ui) alongside Kit USD Agents

Folded-in framing / factual fixes

• Glossary link: /22.08/ → /release/ (always-latest)
• SimReady framing: rewritten to be honest about current status while clear on direction. Was: "a standard and ecosystem for physically accurate 3D assets..." Now: "a specification and ecosystem for physically accurate 3D assets... Currently NVIDIA-led, designed to evolve toward multi-vendor adoption and shared industry standards. The intent: simulation-vertical requirements that are shared and validatable across the ecosystem, not vendor-private." Second paragraph keeps the physical-AI direction.
• USDA description: "ASCII-formatted USD" → "human-readable USD" (USDA accepts UTF-8; "human-readable" captures the format's intent more directly).

Out of scope (next iteration)

Saved for follow-up PRs to keep this one focused:

• Section restructure of ## How Do I Optimize? and ## Best Practices into decision rubrics (file-format / composition / runtime / asset-structure layers)
• Common Pitfalls subsection consolidating scattered anti-patterns as DON'T → DO → because triples
• Top-N code snippets (lift-and-paste examples for usdchecker invocation, opening a stage, USDRT prim query, point-instancer creation, assetInfo read/write)
• Companion docs/openusd-cheatsheet.json — same content as structured data, ingestible by MCP servers / RAG pipelines without parsing markdown
• MCP server URLs — listed by name only in the Agents section; need verified GitHub or docs URLs

Implementation notes

• Tag vocabulary lives in the HTML comment metadata at the top of the file; intro paragraph mentions tags briefly so casual readers don't ignore them.
• Tags are intentionally short, bracketed, and backticked to stay grep-able and stable across renderers (GitHub, Sphinx, internal docs builds).

[jshrake-nvidia]

This looks good to me. I audited all the tags against the links and everything makes sense.