DOCSTOOLS-6553: document audience-specific content

[goldserg]

Tracker: https://st.yandex-team.ru/DOCSTOOLS-6553

Summary:

• document singular human and agent visibility values
• document agent HTML, Markdown companion, and JSON requests
• document fail-closed rendering and YFM023 validation

Dependencies:

• DOCSTOOLS-6553: add audience-specific visibility transform#1061
• DOCSTOOLS-6553: validate visibility audiences yfmlint#90
• DOCSTOOLS-6553: build audience-specific outputs cli#2250

Apply after the package releases are available.

[github-actions]

✅ Documentation build

Revision built successfully
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Build logs

Warnings (2)

⚠️ en/guides/openapi.md: 168: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 265] [Context: " — the specification is displayed directly on the page (default value). If the size of the specification's json schema exceeds the value of ##maxOpenapiIncludeSize## (100 KB by default), the mode automatically switches to "]

⚠️ en/tools/docs/build.md: 52: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 109] [Context: " — a snapshot of the dependency graph (pages, included files, assets, missing paths, edge count), as well as "]

[github-actions]

✅ Documentation build

Revision built successfully
Revision preview link

Build logs

Warnings (2)

⚠️ en/guides/openapi.md: 168: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 265] [Context: " — the specification is displayed directly on the page (default value). If the size of the specification's json schema exceeds the value of ##maxOpenapiIncludeSize## (100 KB by default), the mode automatically switches to "]

⚠️ en/tools/docs/build.md: 52: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 109] [Context: " — a snapshot of the dependency graph (pages, included files, assets, missing paths, edge count), as well as "]

[github-actions]

✅ Documentation build

Revision built successfully
Revision preview link

Build logs

Warnings (2)

⚠️ en/guides/openapi.md: 168: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 265] [Context: " — the specification is displayed directly on the page (default value). If the size of the specification's json schema exceeds the value of ##maxOpenapiIncludeSize## (100 KB by default), the mode automatically switches to "]

⚠️ en/tools/docs/build.md: 52: YFM001 / inline-code-length Inline code length [Expected: 100; Actual: 109] [Context: " — a snapshot of the dependency graph (pages, included files, assets, missing paths, edge count), as well as "]

[martyanovandrey]

"The regular HTML and Markdown output includes common and human content ... markers are not included in either result" does not match the build: none of these PRs touch output-md, so yfm build -f md keeps both bodies and the raw ::: markers verbatim, which I checked on a fixture. That is intentional so translation and the viewer can filter later, but the sentence promises the opposite. Reword it to say markers survive in md output on purpose, and keep the "stripped" claim for html and llms-full?