Design: workload ownership and migration to owner repos

Workloads currently live in the core-tools repo. For GA, each workload
should live with its owning team (templates in templates repo, workers
in worker repos, host in host repo) so they release together. Design
the publisher onboarding story and the migration plan before moving any
code.

## Definition of Done

- [ ] Publisher onboarding doc: per-repo CI, feed publishing, version
alignment, release coordination
- [ ] Migration plan per workload (templates .NET/Node/Python, workers
Node/Python/Java/PowerShell, Host)
- [ ] Owner sign-off captured from each target repo team
- [ ] Follow-up migration issues opened in each owner repo
- [ ] Core-tools repo retains only the thin CLI + shared workload
infrastructure

Start by reviewing the publisher onboarding requirements and the workload list: templates, workers, and Host. Document per-repo CI, feed publishing, version alignment, and release coordination; then create a migration plan for each workload, capture owner sign-off, and open follow-up issues in each target repo. Done means Core-tools retains only the thin CLI and shared workload infrastructure.

Written by the indexing model from the issue text.