teach epic-create/migrate-repo the resolved epic home (#621)
Amend the epic-create and migrate-repo skills for visibility-based epic homes (epic #130): the epic home is derived from repository visibility and the create/report commands take an explicit --repo target that echoes the resolved home (/.github for a public repo, the repo itself when private). Updates the epic-create Preflight, Overview, and the create/spec workflow steps, and the migrate-repo Preflight and ad-hoc setup step. Scoped to the routing edits; the separate pipeline-encoding work is #606. Task of epic #130.