[doc-only] docs: Add the v2 migration guide to a toctree - #3387

No shared Lychee authored cache was restored for this checker configuration. Checking links without this baseline may take longer and make more network requests. This is expected after checker changes in a PR; a refresh on main cannot seed settings that exist only in a PR. For an unexpected miss on main, maintainers can run CI: Lychee checks and caches (lychee.yml) on main with refresh-cache enabled. https://github.com/NVIDIA/cuda-python/actions/workflows/lychee.yml

emSign ECC Root CA - G3 on 26.04: already fixed (ca-certificates 20260816ubuntu0.26.04.1)