Reorganize documentation and setup repo for Eng.ms compatibility

[GeorgeNgMsft]

This PR reorganizes our documentation folder to be compatible with Eng.MS. It also establishes a new wiki structure combining a mixture of authored documentation (overview, architecture, etc) and auto-generated docs from the packages/agents (README.Autogen.md, etc).

Example wiki view from local DocFX server

• Conceptual content (overviews, the architecture map, this contributor guide, templates) is hand-authored here under ts/docs/.
• Architecture deep dives are native files under ts/docs/architecture/**, grouped into sub-directories — the former Design tree now lives in architecture/workflows/. They are edited in place; the DocFX build reads them directly, with no second copy.
• Package and agent reference is sourced from each package's own README.md and its README.AUTOGEN.md companion (produced by the doc-autogen pipeline) and staged in at build time. A generator keeps the navigation in step with the filesystem so a newly added package or agent shows up automatically.