fix(ci): move docs deploy workflow to top-level .github/workflows (#539)

GitHub only recognizes workflows under the repository root's
.github/workflows/ directory. The deploy-docs.yml was nested inside
docs-site/.github/workflows/ which GitHub ignores.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jamesadevine