[Task]: Add API reference publishing from XML docs

[rian-be]

Summary

Add repeatable workflow for generating and validating API reference documentation from the repository's XML docs using DocFX.

Goal

Turn the existing XML documentation coverage into publishable API reference so the public surface of the library and its governance packages is easier to inspect and keep current.

Problem

The repository already exposes a broad public API surface, but the documentation workflow was still manual. As the public surface grows, manually keeping API docs in sync is error-prone and easy to postpone.

XML docs are now enabled for the public packages and DocFX is used as the source of truth for the generated API reference. The missing piece was a clear repo workflow that turns those docs into a consistent reference artifact and keeps that artifact discoverable during local development and CI.

Scope

• Add workflow for generating API reference content from XML documentation
• Define which projects and namespaces are part of the published API reference
• Make the output location fit the existing Docs/API structure
• Add repeatable local command or task for regenerating the reference
• Keep the workflow compatible with the repository's current documentation organization
• Document how contributors should update API reference content after public API changes
• Avoid coupling API reference generation to release packaging unless strictly necessary

Design Expectations

• The workflow should source from XML docs rather than from hand maintained prose where possible.
• Generated reference content should be predictable and easy to review in diffs.
• The process should be simple enough to run locally before opening PR.
• The documentation layout should stay aligned with the current Docs/API directory.
• If manual curation step is needed, it should be minimal and explicit.

Suggested Deliverables

• A documented API reference generation command
• Updated Docs/API content produced from XML docs
• Clear instructions for contributors on when and how to regenerate the docs
• Optional CI validation that the reference is current

Acceptance Criteria

• The repository can regenerate API reference documentation from XML docs through repeatable command
• The published reference maps to the current public API surface of the repo
• The output is placed in or aligned with the existing Docs/API structure
• Contributors have clear path for updating API docs after public API changes
• The workflow is maintainable and does not require hand editing large generated sections

Non-Goals

• This issue does not redesign the docs site or docs theme
• This issue does not change runtime behavior
• This issue does not require every internal type to be documented publicly
• This issue does not force release packaging to depend on docs generation

Notes

DocFX now builds the site from docfx.json, and CI validates the docs build in the PR workflow.