test(vocabulary): establish the public terminology baseline

[aaltshuler]

Summary

Adds the reviewed vocabulary inventory baseline at tools/omnigraph-vocabulary-guard/graph-vocabulary-inventory.tsv.

Surface	Observations
Route-reachable OpenAPI	94
Public-facing Rust text	1,087
Rendered user docs	528
Public Rust signatures	281
Total	1,990

This changes no runtime behavior or public contract. It lands separately so the stacked guard must compare against an established merge-base inventory instead of bootstrapping and approving its own initial state.

Stack

• Base: main
• Follow-up: graph vocabulary guard and presentation convergence
• The follow-up remains based on this branch until this baseline lands.

Governance

This PR is intentionally Draft. There is no accepted tracking issue or formal RFC authorizing the broader vocabulary work; do not merge the stack until that requirement is resolved.

The internal working RFC remains ignored under docs/internal/ and is not included in either PR.